Hi
This may happen due to two following reasons:
a) Mozilla Firefox may be running and it is not responding at all
b) ~/.mozilla directory is corrupted while updating or installing an extension
Mozilla Firefox may be running and it is not responding at all
First see if Firefox is running or not by typing following command:
$ ps aux | grep firefox
Ouput(or something like that):
deusdara 1663 9.9 11.7 778224 238120 ? Sl 11:39 0:30 /usr/lib/firefox/firefox
deusdara 1866 0.0 0.0 4988 868 pts/0 S+ 11:45 0:00 grep --color=auto firefox
If a process is running, kill it by typing:
$ kill 1663
OR
$ killall firefox-bin
Now try to start Firefox
~/.mozilla/firefox directory is corrupted while updating or installing an extension
Just rename a ~/.mozilla/firefox directory
$ mv ~/.mozilla/firefox ~/.mozilla/firefox.old
Now try to start Firefox.
What happens when you try to launch firefox from command line? Eg. type firefox in terminal.