So I found what turns out to be only one source:
The license for the extension is MPL 1.1/GPL 2.0/LGPL 2.1.
CaveatVersion 0.2.4 officially works in Firefox 1.5, but here are instructions in a 18.01.2007 comment to a blog post on similar matters. (The original text was here.)
Instructions in my own words: Download the XPI file (the lowermost is the newest version; if you are not sure, then check the statusbar when mousing over the 0.2.4 file link), extract it into a folder, open
install.rdfwith an editor that supports CR & LF linebraks (NotePad2 is ok); there, edit the
em:maxVersionparameter value from
2.0.0, compress the decompressed files, then rename the file's
.zip(I assume) extension to
.xpi, then move the file into an open Firefox window to install. When recompressing, make sure that you're only compressing the selected files and folders within the extracted folder and not the folder itself.