Try resetting the settings in Firefox, hopefully you can complete the steps before it becomes unresponsive. To do so, go to the new config menu, open the Help menu, and then Troubleshooting Information. Click Reset Firefox.
Firefox will reset all your data (including addons, themes and profile data), and your Firefox installation will be like a brand new one (without the hassles of uninstalling and reinstalling the product, which anyway will continue to use the old settings and profile information). If everything works fine, then you can re-install your favorite addons.
Otherwise, you could try deleting (or backing up) your profiles directory, which is housed in $HOME/.mozilla/firefox.