We're on track with version 3.5.6. Again, we link to our howto for firefox-3.5.1. The only difference are the sources. And I will offer the binaries of course.
You can get the sources of version 3.5.6 at ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.5.6/source/. You need to download ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.5.6/source/firefox-3.5.6.source.tar.bz2 (perhaps you need a right-click here to get it).
The sources are compiled as I described in Firefox 3.5.x Community Build for PowerPC Linux Update 3.5.1.
If you prefer to use the binary, it's here: firefox-3.5.6.en-US.linux-powerpc.tar.bz2
If you need information on how to use the binary, please refer to Firefox 3.5.x Community Build for PowerPC Linux Update 3.5.1.