The two forks of Pale Moon for Windows XP

This was posted as a reply at Google Product Forums. This concerned video stopping every 25 minutes on YouTube during HTML5 playback.

I got to test a long-form YouTube video with New Moon 27.6.0a1, and the 25-minute video lag still happens.

At that point (when video stops during playback), I pause, or move the video progress indicator back a little to keep the video going.
I treat the breaks every 25 minutes like the breaks during tv ads

I'm most likely stuck with that video lag stoppage, as I've chosen to keep a fork of Pale Moon Moon 27.6.x, because that branch still supports cookie prompting.

There are two forks of Pale Moon for Windows XP:

* New Moon — available at RT's Free Soft blog at Blogspot.
This browser is not my main driver.
* MyPal. Of the two, MyPal 27.6.2 is a somewhat later release than New Moon 27.6.0a1, so I just might consider replacing New Moon with MyPal.

The positive side is, that unlike Firefox, the forks support H.264 video, which should play most videos on YouTube, and clips on twitter.

To switch on support for WebM/VP9 in New Moon 27.6.0a1, one can uncheck "Use MSE asynchronously", and then check "Enable MSE for WebM video" in the Content section of the Options window.

Newer versions of forks most likely have H.264 support as built-in. Older versions of New Moon require extracting the lav extension file(s) from lav.7z into the folder where the browser is installed in Program Files.

It should be noted, that New Moon and MyPal 27.6.x are older versions, but support a few bits more functionality than a comparable version of Firefox (38.8).

Uploading files via Firefox in Android 2.3

This is very much a quick-and-dirty post, so that I wouldn't forget about it. As my phone is also currently charging while off, I can't check out some information pertaining to this post. Some time after the phone will have charged, I'll update this post accordingly.

So, yesterday, I had this need to upload a file to a project in Github via Firefox in Android 2.3 Gingerbread.

Now, Github is quite a modern website, and in Android 2.3, the logical browser for visiting Github and other state-of-the-art sites is Firefox for Android or a derivative, such as GNU IceCat, Orfox, or Adblock Browser.

I have two browsers in my phone: GNU IceCat 38.8 and Firefox 44.0. Both have NoScript installed, and Github servers were whitelisted in both. Separate issues with uploading are covered at the end of this post.

The crux of the problem is having a filepicker that works.

Typically, an Android user gets a file activity dialog to pick an app through which to select a file; such as Gallery for photos and videos, or somesuch.

For a simple text file, things are a bit more complicated, but I've discovered two kinds of filepickers that I associated with after having installed two separate apps.

• One filepicker, "Choose file" with blue folder icons, seems to be related to VimTouch, a version of Vim for Android, because I noticed that filepicker after installing this great text editor.
• Another filepicker, "Find file" or "Find command" (I might err with its title) is adorned with the Terminal Emulator icon.

Both VimTouch (alternatively spelled 'Vim Touch') and Terminal Emulator were installed through F-Droid, a repository of free and open source apps for Android.

The filepicker that works, is the one I associate with Terminal Emulator.

Unfortunately, I don't know beyond my memory of my app installation activities, and beyond one app icon about how to find out which app or handler these two particular filepickers are actually associated with.

Upload issues.

Resolved on 28.04.2017.

With IceCat, there were issues relating to uploading files to GitHub, whereby file upload failed with an error. File upload to GitHub worked with Firefox for Android, but for some odd reason, did not work in IceCat.

Now, I use NoScript in Android Firefox and in IceCatMobile (based on Firefox with very small changes). Since both have slightly different NoScript whitelists, then I attributed the issue to an incomplete NoScript whitelist in IceCatMobile. But it was not at fault, and the problem was much simpler, though no less esoteric.

Turns out, that all other things being almost equal, GitHub does not recognise the Firefox-based GNU IceCat browser when uploading files, if an IceCat-only desktop user-agent (UA) string is used.

The solution is to change in IceCat's about:config page the Gecko-based user-agent override affecting the Github domain to that of Firefox, leaving the version number intact.

<Moot:> Possible issues wrt NoScript

The reason for that, is, that I edit NoScript whitelists in Vim Touch so as to get a very fine-grained whitelist on a subdomain level (3rd-level domains and below, such as sub.domain.tld ), because the browser extension in Android does not provide such functionality.

The rationale for subdomain-level whitelisting is, that my phone is rather underpowered, and subdomain-level whitelists in Firefox/derivatives make it possible to allow advanced site functionality, and at the same time, to block script-based ads and trackers. In addition, it's possible to switch off very resource-intensive site functionality by blocking certain subdomains of a website. Such features are impossible in the stock Android browser, the rendering engine of which dates back to 2011.

(I'm often contemplate writing a separate post about all that.)

So, the NoScript whitelist for IceCat is typically more fine-grained; yet oddly, file upload to Github actually worked with Firefox.

Independence Day: Resurgence website and Firefox

A quick post: www.warof1996.com might not display in Firefox and other Gecko-based browsers.

The reason is that the site is based on WebGL, and Firefox blocks WebGL, if the GPU (video card) driver is out of date or does not support WebGL.

The solution in Windows is to update GPU drivers either through the computer manufacturer's website or through the site of the GPU supplier — one of Intel, nVidia, or AMD/ATI, but not limited to only these.

Thorough care should be taken to match the driver to the correct display adapter model.

If that doesn't work, the GPU is too old, or EOL'd.

I strongly recommend not to force Firefox to use WebGL, because this move can damage hardware.

The alternative is to use Google Chrome or Chromium, which probably uses a CPU-based workaround; but if either the graphics adapter or the CPU or both are too old, then rendering is unlikely to work, or is too slow.

> Explanation — contains minimum driver versions that support WebGL.

In addition, visit about:support in Firefox and the Graphics section therein, which also recommends the minimum driver version for WebGL (Direct2D, etc). The posting contains the same warnings about possible damage to hardware if Firefox were forced to use WebGL.

System requirements

This table is incomplete. I've only gotten to test the website on three computers (with some reservations), and gotten an external report about another.

PC	Hardware/software specifications
	CPU	GPU	RAM	OS	Fx	Chrome	Notes
ASUS K53SC notebook	Intel Core i3 2310M @ 2.1 GHz, dual-core	i:Intel HD Graphics 3000 d:nVidia GeForce GT 520MX	4 Gb DDR3, 665.1 MHz	Windows 7 SP1	Yes	Yes	Required driver updates: I had to upgrade both Intel and nVidia drivers through downloading them from their respective websites.
ASUS U46SV	Intel Core i5 2410M @ 2.3 GHz, dual-core	i: Intel HD Graphics 3000	8 Gb	Windows 10 (build unknown)	Slow	Not tested	Website opens, but performance is slow and jerky, and the fan began working intensely.
	d:	nVidia GeForce GT 540M
ThinkPad R60e (0657-3WG)	Intel Core Duo T2400 (Centrino)	Mobile Intel 945GM Express	2 Gb DDR2 (an upgrade from just 512 Mb)	Windows XP SP3	No	Slow / ok	Rendering was slow, but the site was usable. Chrome: 48.0.2564.109 32-bit; Blink 537.36 JavaScript: V8 4.8.271.19, (This version already announced that it's to be retired on Windows xp.) Instead of OpenGL, Chrome's default renderer in Windows is ANGLE, which translates OpenGL ES to Direct3D, as it has better driver support. Thus, results for Chrome can differ.
hp dv5204ea notebook	Intel Celeron M 410 @ 1.46 GHz	Mobile Intel 945GM Express	1 Gb DDR2, 266 MHz	Windows XP SP3	No	Too slow	While I did upgrade the driver, its version is still less than required: The latest Windows XP driver for this GPU is 6.14.10.4926 (15.02.2008), but Firefox wants at least version "6.1400.1000.5218".
PC	CPU	GPU	RAM	OS	Fx	Chrome

All this does not yet indicate much as to what the titular website's actual system requirements are. In notebook computers, the default video card used by any program in Windows is the integrated adapter, while nVidia software provides an option to launch programs using its own GPU.

The Asus notebook with greater specifications falls below the threshold, whereas the Asus notebook with slightly lesser specs, an older operating system and updated video drivers shows the website nicely.

ID-kaardi tarkvara seadistamine modernses SeaMonkey lehitsejas

Modernse SeaMonkey lehitseja (näiteks versioon 2.6 ja uuemad) ning ID-kaardi tarkvara töölesaamine on omaette teema, mille kohta ma leidsin, et see vajaks eraldi käsitlust, sest kõik kohe tööle ei hakka. (Nimelt ID-kaardi tarkvara installer end SeaMonkey jaoks õieti ei seadistagi, seega osa asju tuleb käsitsi teha.)

Üldised tingimused, millega kogu krempel tööle õnnestus saada:
* Windows XP (SP2 või uuem; näiteks). Opsüsteemide suhtes tuleks olla siiski suhteliselt agnostiline;
* SeaMonkey 2.6 (ingliskeelne) — on tõepoolest vanem versioon, aga mitte nii vana kui 1.1.xx), seega SeaMonkey 2.xx;
* Oletame, et NoScript ei ole Firefoxis või SeaMonkey-s peal. (ID-kaardi ja NoScriptiga on veel täiendavalt igast jama.)

Nüüd.. eeltingimused peaksid olema sellised:

* ID-kaardi lugeja draiver peab olema installitud; soovitatavalt kõige uuem, mis vastavale opsüsteemile valmis tehtud;
* ID-kaardi tarkvara peab olema kõige uuem, juba peale installitud ning peaks näiteks Firefoxil töötama. Firefoxist veidi allpool, isegi kui tegemist ei ole kasutaja vaikimisi lehitsejaga.

Kuigi ametlikult on toetatud Mozilla Firefox, siis oletatavasti installib ID-kaardi tarkvara kaasaegne versioon EstEID Firefoxi plugina sellegipoolest Windowsi opsüsteemis pluginate üldisesse kataloogi. Sealtsamast kataloogist leiavad Gecko-põhised lehitsejad kõik pluginad automaatselt üles.

Tulemuseks peaks SeaMonkey' pluginate nimekirjas olema

EstEID Firefox Plug-in 3.7.1.1009

Kui see on olemas, siis on pool tööd juba tehtud.

Kui EstEID pluginat SeaMonkey pluginate nimekirjas pole, aga Firefoxis on, siis SeaMonkey-s peaks minema aadressiribal asukohale about:plugins — See peaks panema SeaMonkey ning teised Gecko-põhised lehitsejad otsima üles kõik olemasolevad ja võimalikud pluginad, mis opsüsteem pakub.

Siit edasi tulevad toimingud, mida Firefoxile tehakse automaatselt, aga mis SeaMonkey-s tuleb "käsitsi" teha:

• Laadida PIN-koodi küsimise moodul turvaseadete hulka:
  Edit > Preferences > Privacy & Security > Certificates > Manage Security Devices nupp:
  Device Manager akna vasakpoolses Security Modules and Devices nimekirjas peaks olema

  Estonian ID Card
 Virtual hotplug slot
 OMNIKEY CardMan 1021
  antud kaardilugeja mudel ^ on Eestis üks levinumaid, aga võib olla ka mõni teine.

  Kui seda pole (milles võib SeaMonkey puhul suhtkoht kindel olla), siis
  * vajutada vasakult nupule Load ja
  * uues aknakeses pealkirjaga Load PKCS#11 Device sisestada
  * Module Name: väljale
  Estonian ID Card
  * Module filename puhul ma annan praegu ette mooduli asukoha, mille leidsin Firefoxist:
  C:\WINDOWS\system32\onepin-opensc-pkcs11.dll
  Selle rea võib sinna nii asetada või kasutada Browse nuppu ja leida moodul failikorjajaga niimoodi üles ja sisestada. Vajutada OK. Device Manager aknas peaks uus moodul nähtav olema ning vajutada OK. Preferences aknas vajutada OK. Teha SeaMonkey-le restart.
• Edasi tuleb panna SeaMonkey-le kõik Sertifitseerimiskeskuse sertifikaadid. Need on saadavad siit:
  https://www.sk.ee/Repositoorium/SK-sertifikaadid/juursertifikaadid
  Põhimõtteliselt tuleks näiteks tirida sertifikaatide PEM-lingid uuele vahekaardile ja lubada igaühele autentimine vähemalt veebisaitidele [teine ja kolmas linnuke on vastavalt e-postile (e-mail) ja arendajatele (developers)]. Iga sertifikaadi puhul vajutada OK. Mõnedel juhtudel on osad sertifikaadid juba installitud ja SeaMonkey annab sellest lühikese teatega väikeses aknakeses teada. Teha lehitsejale restart.

Põhimõtteliselt peaks asi nüüd töötama.
Et järele vaadata, kas seadistus töötab, minna aadressile
https://digidoc.sk.ee
ja siseneda ID-kaardiga.

Täiendavad seaded:
Preferences > Privacy & Security > Validation —
Aktiivsed peaksid olema järgmised seaded:
[\/] Use the Online Certificate Status Protocol (OCSP) to confirm the current validity of certificates;
(*) Validate a certificate if it specifies an OCSP server.
Need seaded ^ peaksid olema vaikimisi sees, aga igaks juhuks tuleks üle kontrollida.

Mozillale NoScripti installimine Windows Vistas

Seesinane on siis eestikeelne kokkuvõte oma varasemast ingliskeelsest blogipostitusest. Alguses kirjutasin selle kohta ühele sõbrale, ning kuna tekst osutus siiski pikemaks, leidsin ma seejärel, et jutt vajab avaldamist.

Hiljuti ühes Windows Vistaga masinas avastasin Mozilla 1.7.13. Tegemist on siis tarkvarapaketiga, mille lehitsejamoodul on sama vana kui Firefox 1.0.8 (Aprill 2006; esitlusmootor pärineb 2004. aastast ja Mozilla enda arhitektuur 2001.-st aastast).

Et Mozilla mõnede lehekülgede JavaScripti pärast kokku ei jookseks, läks alguses palju aega, et kuidas sellele NoScript nii peale panna, et töötaks, sest umbes sama vanale Firefoxile Knoppix 4.0.2-s (2005) sai küll. Lõpuks jätsin asja katki...

Mõni kuu hiljem leidsin lahenduse (Mozilla tuli käima panna administraatori õigustega) ja siis panin peale NoScripti, aga nii, et see tuli kindlasti installida Mozilla kasutajaprofiili kataloogi.

SeaMonkey 1.1-ga sellist probleemi ei tohiks olla, sest SeaMonkey 1.1 ja Windows Vista arendus/väljalase langes umbes samale ajale, et põhimõtteliselt sai seda Vista jaoks siis veel kohendada nii, et oleks parem ühilduvus.

SeaMonkey 1.1.19 on üks viimastest vabatarkvaralistest graafilistest lehitsejatest, mis töötab Windows 98/Me peal.

Cannot play videos on Yahoo! News?

Symptom: This often happens with users of Firefox and other Gecko-based browsers, when:
• they can't show most news videos on the Yahoo! News website and some other Yahoo! properties;
• the commenting system is not functional (can't properly view and post comments).

Privacy-conscious users, and/or those who wish for their browsers to consume less resources, use a script blocking add-on, such as NoScript. I often have NoScript configured to allow/disallow full domains (like d.yimg.com) and not just second-level domains (just yimg.com).

As it often happens, allowing only full subdomains instead of just second-level domains brings with itself more issues.

By default, NoScript includes a whitelist of second-level domains without which major services' functionality would be wholly disabled. The whitelist also contains yahoo.com, yimg.com, and yahoopis.com). The instructions herein are for users who have chosen to impose a more fine-grained control over the websites they visit.

Right, well, I finally played around with NoScript and found a solution:

NoScript:

In addition to news.yahoo.com and screen.yahoo.com and maybe others, allow the following domains essential for video playback:
• l.yimg.com
• d.yimg.com
• connect.facebook.net (If you're privacy-conscious, then allow temporarily).
  
  
11.07.2012. Update: I later discovered that non-video news items also featured videos, so here's an addition of domains that must be allowed:
• video.query.yahoo.com
• yep.video.yahoo.com
• yui.yahooapis.com (important on other Yahoo properties, even if not using video)
• webplayer.yahooapis.com

Flashblock:
• Allow d.yimg.com

^ Including only that domain in the Flashblock whitelist will have the video area rendered with the Flashblock placeholder. Clicking on it will start playback (note that ads are also played).

• Allow l.yimg.com

^ In regular news items that included video, disallowing l.yimg.com wouldn't even load the Flashblock video placeholder.

If you want video to load automatically, allow the above domains, and news.yahoo.com and screen.yahoo.com (and/or other Yahoo! properties as necessary from the Flashblock toolbar button).

Conclusion

Even if l.yimg.com and d.yimg.com are enabled in NoScript, the crucial part for some erroneous coding reason is connect.facebook.net; If that is not allowed, most video code and commenting functionality won't load. Note that connect.facebook.net is the primary culprit. This has been discussed before at forums.informaction.com (a NoScript and web security forum).

Somehow installing, configuring, and using NoScript in K-Meleon 1.5 via Wine

I am assuming that you probably already know how to use Wine and know your way around the computer.

The conditions: Knoppix 4.0.2, because it runs passably with 128 Mb of RAM, in a situation where no swap space is available. This version of Knoppix has a really outdated version of Wine, which makes it difficult to use Windows programs there. There may be people stuck with either that version of Knoppix or that old version of Wine. At least this post provides a case study, which I hope could be of some interest.

The only reasonable place I could find NoScript for K-Meleon 1.5.4 is from extensions.geckozone.org/KMES-NoScriptEn. The version is 1.7.8.0 and it's from 17.06.2008 (that's 2 and 3/4 years old as of April 2011).

First off, change installer's .exe file rights for it to be an executable. Like this from the command line:

chmod u+x "K-Ext(1.1-1.5-1.6)_NoScript(1.7.8.0).exe"
^ u = for current user; + = add/enable; x = executing;
The filename is wrapped in double quotes, because it contains parentheses "()".

In my case, the first round of installation didn't work. Later I specified this target install directory:

z:\mnt\hda1\Program Files\K-Meleon
^ can't remember if I specified an upper- or lowercase letter z

and installation worked after that.

K-Meleon should not be running during installation, so run it after installation.

27.04.2011.–: After a relatively quick-and-dirty article which turned out to be far more specific than originally anticipated and still quick-and-dirty, I've updated the following with information which will make K-Meleon slightly easier to use as it is, with what the setup is and all...

When running K-Meleon through Wine in Knoppix 4.0.2 (remember that it's from 2005 and very outdated) and when you're stuck with such a set-up:

• The NoScript button menu can be used with a mouse by right-clicking on the NoScript button and holding the pointer device button down and dragging the cursor to the necessary command (shortcut menus will otherwise turn off after right-clicking on an item and hovering a mouse cursor over its menu; I've seen this in TWM, don't know how it works in other window managers).
  Other ways:
  • Click on the NoScript button, then use menu hotkeys (underlined) to perform a function;
  • or consider dragging the pointer through the NoScript menu via the main Tools menu.
• Saving configuration changes in the NoScript Options window does not work, because it's impossible to save settings by clicking the OK button, but you can otherwise close the window (saving options may work with newer versions of Wine; haven't tried this myself).
  Workarounds:
  
  • Configuring NoScript is possible only at about:config for settings (use the noscript text pattern in the about:config search bar to get NoScript-specific settings);
  • ^ Consider removing some default domains there from the noscript.default string;
• Worse, the NoScript menu in K-Meleon (at least in the given configuration and set-up) won't show domain names in its menu (Shock! Horror!).
  • Now, the whitelist, which is not shown in about:blank, is only configurable in prefs.js at the local K-Meleon profile folder on the hard drive (from where K-Meleon is run). If you don't know what the prefs.js location of the current profile is, open Preferences, go to "Privacy & Security" preference category, click on the Cache tab and see the "Cache Folder:" entry, which shows the location of the current profile folder.
    An example location is here:
    

    "/mnt/hda1/Program Files/K-Meleon/Profiles/g1bb3r1sh.default"

    So, edit the prefs.js file with a text editor at this line:
     
    user_pref("capability.policy.maonoscript.sites","place.doma.in nam.es here.com in.alphabetic.al ord.er.com ea.ch doma.in na.me separated.wi.th a.space.com and.do not.break.the.li.ne");
     
    Make sure just in case that K-Meleon is not running when editing the file, because if you've saved the file and then exit K-Meleon, then K-Meleon is highly likely to overwrite your changes.
    13.09.2011.

    Given that I had been using K-Meleon like that for a longer while, I created a menu item in the TWM window manager, where I could directly open the prefs.js file from the menu.
  • Alternately, adding sites to whitelists works from the menu (see above), but since the above configuration does not make it possible for the K-Meleon URL bar to function and display addresses, then a user is limited to knowing the site domain and web page address in the following ways:
  • In K-Meleon, the tab bar is typically shown by default, so it should be enough to hover the mouse cursor over a page's tab button: This displays the tool tip, which then shows the site/page title and its partial address.
  • A user might know the site's domain name, if they've entered it themselves (because of limitations, entering a URL goes through editing bookmarks and accessing a bookmark set up for just that).
    A user can specify that only top-level domain names are added, by setting this in NoScript preferences through about:config, only that the whole point of NoScript to me is the fine-grained way in which some subdomains can be whitelisted, so that disruptive ones are duly excluded. Unfortunately, not directly seeing a site's domain name in the URL bar has security implications, including the fact that the non-functioning URL bar doesn't change color when visiting a secure site, though a bottom-right status bar indicator should work. Preferably, only safe sites should be visited. (Avoid clicking e-mail links, if you know they're dubious, but this requires at least some user education and this is where NoScript is useful. There is nevertheless a greater amount of security in running K-Meleon equipped with NoScript, no matter how limited it is, through Wine in Linux than in Windows 9x);
  • Some necessary domain names pulled by a page from (a) differently-named domain/s to fetch scripts and/or stylesheets across sites and subdomains are not displayed anyway (not even in the NoScript menu), so there is no direct way of learning which other domains must be allowed for scripting.
  • Consider disabling NoScript for the duration of the session, if you're using a service which requires logging in and if it's been impossible to learn what are the exact outside domains with necessary scripts.
  • The third option is to import domain names from other NoScript settings in other prefs.js files. This actually works. But what if using a new service that users a non-primary domain name for scripting? Or what if an existing service sometimes changes its subdomains?

pilet.ee-sse ei saa sisse

Juhtus selline lugu, et tegelikult päris modernse, kuid õige pisut aegunud Mozilla Firefoxiga (versioon 3.0.19) läksin pilet.ee kodulehele ning seal tekkis selline veateade:
"invalid security certificate".

Veateade annab võimaluse lisada pilet.ee domeen erandite nimekirja, kuid seda pole tegelikult vaja teha.

Sama veateade võib tulla ka teiste vanemate Gecko-põhiste lehitsejatega, nagu näiteks SeaMonkey (Mozilla edasiarendus), K-Meleon, Galeon, Epiphany jt.

Lahendus:
Tarvis on lehitsejale peale panna Sertifitseerimiskeskuse sertifikaadid siit või siit.

See on suhteliselt lihtne, sest sertifikaatidele tuleb peale klikkida ja siis ilmub programmidialoog, mille kaudu saab sertifikaadid lehitsejasse panna. Saab valida vähemalt, et nende sertifikaatidega saab ära tunda veebisaite.

Tuleb tähele panna, et see protseduur tuleb veateate esinemisel teha igas lehitsejas ja lehitsejaprofiilis eraldi. Lähtuda võib kasvõi sellest, kui lehitsejas niisugune veateade tekib.

Kui niisuguseid asju juhtub ka Internet Exploreriga, tuleb sertifikaat samamoodi peale panna.

Optimize page rendering of Gecko-based browsers

Originally posted on 24.09.2008.

Tips from here.

• nglayout.initialpaint.delay — Set the integer value to 0 if the connection is too slow.
  
  E., 06.12.2010 Edit/Update: The downside is greater CPU usage, so if the computer is slow and/or if there's a slow operating system (Windows 95/98), then don't use this feature.
  
  For example, I have at my wherewithal a 900 MHz computer with 128 Mb RAM and Windows 98SE (the operating system that was supplied by the manufacturer), in which OS the latest Gecko-based browsers can be Mozilla Firefox 2.0.0.20, K-Meleon 1.5.4 and SeaMonkey 1.1.19.
  
  In late 2010 I realized how much more complex have websites become and their rendering really slowed the computer down. Messages about unresponsive scripts have also become more frequent.
  
  The only thoughtful solution to this would be changing the operating system to something lightweight, which supports SeaMonkey 2.0 (such as Linux). More about this in a future post.

Most important settings in optimizing Mozilla Firefox, K-Meleon and other Gecko-based browsers

Usually these two about:config instructions rarely appear together in any entry about optimizing a Gecko-enabled browser, such as Mozilla Firefox, K-Meleon, SeaMonkey and others.

In about:config —
• network.prefetch-next — toggle to false (can be done with a doubleclick)
• browser.sessionhistory.max_total_viewers — change to 0 on computers with low resources or 2 on friskier machines.
In very modern and very fast machines, the default settings can be kept intact.

Update: 28 Coolest Firefox about:config Tricks — Contains instructions both for Windows and Linux users and those who prefer some of the older Firefox UI features.

E., 18.07.2011. Update: Something I very recently found by chance in a version of Firefox on Knoppix 4.0.2, yet which may well exist in other systems and versions:

browser.related.enabled can be set to false, because the preference does very little specifically in anything that is not SeaMonkey (unless someone is using any What's Related-like extension that uses the preference).

Most of the preferences well apply to older versions of Gecko-based browsers, especially those that use Gecko 1.7, 1.8 and 1.8.1 (upwards to Firefox 2, SeaMonkey 1.1 and K-Meleon 1.5.4).

Firefox 4.0/5.0+ (where 5.0 is actually an incremental development because of rapid development practices now at mozilla.org) are less and less likely to require these modifications, because they're typically installed on modern and very modern computers.

L., 22.10.2011. Update:

browser.sessionstore.max_concurrent_tabs — Set to 0

If you're using multiple tabs, then upon session restore all the tabs are restored, but pages are loaded only on the tabs that you open. If you're using more than one window, the last tabs open before closing will still load.

Applies to Mozilla Firefox/Iceweasel/IceCat 4–8 only
08.01.2012. update: The feature was deprecated in version 9.0 of Firefox and corresponding forks. Users who still have version 8.0.1 at most and are happy with how it performs, should turn off the auto-update feature in Preferences.

Other options can be found from about:config entries at MozillaZine Knowledge Base Wiki.

P., 04.03.2012. Update:
This one should be useful for users of LiveCD-s:

plugins.hide_infobar_for_missing_plugin

This should work in Mozilla Firefox/Debian Iceweasel/GNU IceCat 3.0 and SeaMonkey 2.0 or newer (given that the function was first checked in on 02.10.2007).

P., 05.08.2012. Update: browser.sessionstore.interval — Set integer to more than 10000 (milliseconds; default value means 10 seconds) — I sometimes set it to 34000 or even 60000.

This can be useful if you don't want Firefox to interfere with plugin work. (I won't guarantee that it would work as expected, but in theory it sould improve performance. Apply if you think it may help.)