Bug 641842 upgraded the Firefox slaves to gcc 4.5.2, we should do the same (32bit + 64bit). Note that contrary to them, we actually already use gcc 4.5 in live builds on trunk and 2.1, but that should not pose an actual problem. Just Gracefully shutdown buildbot before doing the upgrade and clobber the machines afterwards. :)
This bug is now irrelevant since everything is now 4.8+ and puppetized and with the recent move to using tooltool packages.