If I try to launch firefox I get:
Bus error (core dumped)
When, until last week, I had Gnome 12.04 it was the same... then, during the upgrade (I now have 14.04) Firefox started working (without Flash Player). I installed Flash Player and Firefox stopped working.
Since I am no expert at all, in this answer I honestly don't understand what does "Simply activate it by going to System Settings>Software Sources>Other Software and check the boxes for Canonical Partners" mean (I have the box for Canonical Patners checked, if that is).
I tried the following things found on the Web:
firefox -safe-modeit's the same
sudo dpkg --purge --force-all firefox, then
sudo apt-get install firefox, nothing.
Disinstalled Flash Player, useless
Like suggested here,
rm -r ~/.mozilla. Too bad for me.
Then nothing removing