The "Firefox4" repositories for Fedora 13 and Fedora 14 have been updated to 4.0.1:
I have created a "Firefox5" repository for Fedora 15 (currently at beta3). Just like the firefox4 repo, this provides xulrunner5 and firefox5 packages which install in parallel to the system xulrunner/firefox. I have no plans to backport this to Fedora 13 or 14, because that would mean that there would be a situation with three different copies of Firefox on the system at the same time. If you want to rebuild for older targets, go nuts.