Firefox 3.6.x (Mac OS X 10.4 and later) can be found here:

• http://www.mozilla.com/en-US/firefox/all-older.html
• http://www.mozilla.com/firefox/3.6/system-requirements/

[https://support.mozilla.org/en-US/kb/Installing%20a%20previous%20version%...] Before you download an earlier version of Firefox, read Mozilla's caveat (above).

Which has a link to the following Mozilla website of downloads for recent and old versions of Firefox: Install-older-version-of-Firefox

since this question is still getting a lot of traffic - firefox 3.6.28 unfortunately was the last version of the browser which supported mac osx 10.4.11 and the powerpc architecture.

there's the tenfourfox project which is porting the up-to-date version of mozilla's browser to powerpc. the downside is tenfourfox doesn't support plugins like flash or java. for more information see: www.floodgap.com/software/tenfourfox

Firefox no longer works with Mac OS X 10.4 or PowerPC processors

Note that TenFourFox only works with a Power PC processor and not with an Intel processor that the original poster has.

None of links I tried for Mac on the page http://www.mozilla.com/en-US/firefox/all-older.html are working. But I found a version on the FTP server: https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.6.28/mac/

Thank you so much! I clicked on the en-US link and I got my old version of Firefox back with bookmarks intact. xoxoxoxo