Annoyingly, I was hit with a problem after an update via update-manager on Ubuntu.
Firefox just wouldn't start and when I invoked it via a korn shell, I received the rather terse error 'Bus error' and nothing else. How wonderfully educational.
I took the option of installing Galeon, and then got hit with the same error. In the end, I installed Lynx (great text browser) and had a poke around.
My eventual 'solution' was to check the updates history, and then uninstall Firefox via Synaptic. Some of the related programs that were uninstalled were ubifox and xulrunner.
Afterwards, I was able to start Firefox again - to my relief.