Linux repositories=I mean in general. So why aren't there any newer version of Firefox available in the repositories? [Fedora, Ubuntu, etc.]
Why are there Firefox 3.6 in the Linux repositories
firefox;repository
That's simply not true.  I'm posting this from FF 8.0.1, installed directly from the repos (Arch), and at work I have 8.0 (Ubuntu 11.10).Ubuntu (and maybe others) sets in stone the major versions of the software in each release's repo at its release, so that no incompatibility arises if one package doesn't support another's new major version and it doesn't get caught before making the repos.  They do, however, backprop bug and security fixes.  And even on Ubuntu you have to go back to Maverick/10.10, over a year old, to find FF 3.6.