- Mozilla Firefox 188.8.131.52 (Gecko 184.108.40.206, 20081217),
- K-Meleon 1.5.4 (Gecko 220.127.116.11pre, released on 05.03.2010) and
- SeaMonkey 1.1.19 (Gecko 18.104.22.168, released on 16.03.2010).
The reasons are thus:
- Under similar limited circumstances, SeaMonkey 1.1 is more responsive than Mozilla Firefox 2.
Here's why: SeaMonkey 1.1's XPFE/XPToolkit-based user interface (UI) technology dates back to Mozilla Application Suite (v1.0 released 05.06.2002, but pre-releases were usable since a year before), while Mozilla Firefox 2.0 (2006) is completely based on a newer toolkit (XUL).
- SeaMonkey 1.1.19 has a newer and more secure Gecko layout engine than Mozilla Firefox 22.214.171.124 and K-Meleon.
- SeaMonkey 1.1 has been supported by the two most important extensions to grace web surfing: Flashblock and NoScript.
K-Meleon also uses the native Windows API for its UI, meaning that it can't run extensions which normally work in SeaMonkey or Mozilla Firefox.
The only caveat is that SeaMonkey requires at least 64 Mb of RAM to run passably and at least a 266 MHz CPU. Well, a Navigator-only one-window/one-or-two-tab solution works in a PC with just a slightly lesser CPU.
K-Meleon is best for computers with 32–48 Mb of RAM (certainly less than 64 Mb).
On PluginsAlthough Adobe Acrobat Reader 6.0.6 (released/updated last in 2003) is about the last version for Windows 98 as far as I know, it is still outdated and so more vulnerable to attacks that use the Reader.
While older computers might best handle even older versions of Acrobat Reader, it's most important to disable Acrobat (Java)Script in the Reader's preferences, no matter the version. This should somehow prevent malicious websites using the Reader as an attack vector.
A complete alternative to using Adobe Reader in old computers is muPDF: It's much less resource intensive, supports the newest PDF document display standard (PDF 1.7) and does not use AcroScript. muPDF does not support interactive PDF elements; this is both a caveat and a security/speed measure. muPDF does capture the file type association in Windows, so when using the app, then it's an either-or situation between it and Acrobat Reader. It should still be a no-brainer in old computers.