This past weekend I installed the April 2nd 4.9 snapshot on my ancient Pentium I laptop - and then downloaded and installed the mozilla-firefox-3.6.16p0.tgz package with its dependencies.
As far as I can tell X and Firefox now seem very stable. No crashes after several hours of browsing. About a month ago (see March posts) I couldn't do that even 5 minutes. Thanks very much to someone for finding and fixing this! Mike Beasley