We missed 3.6b4 for a reason. I assumed that it will only be days before 3.6 will be released. And now it's another beta before years end. So I compiled Firefox 3.6b5 for your PowerPCs out there. I will only link to our howto for firefox-3.6. The only difference are the sources. And I will offer the binaries of course.
You get the sources of version 3.6.beta5 at ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.6b5/source/. You need to download ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.6b3/source/firefox-3.6b5.source.tar.bz2 (perhaps you need a right-click here to get it).
The sources are compiled as I described in Firefox 3.6.x Community Build for PowerPC Linux.
If you prefer to use the binary, it's here: firefox-3.6b5.en-US.linux-powerpc.tar.bz2
If you need information on how to use the binary, please refer to Firefox 3.6.x Community Build for PowerPC Linux.
And please watch out. It is still Beta!