(Emphasis added.)[...] I uninstalled FF3, wiped out my profile, and reinstalled, and everything's worked fine since. [...]
This is an important portion to point out for everyone to read. Uninstalling a Firefox installation then reinstalling won't fix anything in most cases, because the new installation is going to use the exact same profile as the old installation. One would also need to delete the profile after uninstalling Firefox in order to have any result after reinstalling. This may not apply, of course, if it's a specific extension or several extensions causing the issue.