Mozilla Firefox is not opening

This may sound strange, but sometimes Mozilla Firefox does not open. Click the Firefox icon and nothing happens. So how can you fix the, if Mozilla Firefox is not working?

This can occur for the following reasons:
a) Mozilla Firefox may be running and not responding at all
b) ~ /. Mozilla is corrupted during upgrade or installation of an extension

Mozilla Firefox may be running and it is not opening at all

First see if Firefox is running or not by typing following command:

$ ps aux | grep firefox

Ouput:

abcd     3174 19.5 13.9 209040 107008 ?     S    20:17   7:30 /opt/firefox/firefox-bin

If a process is running, kill it by typing:
$ kill 3174

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.
Please note that you can apply above procedure to other Mozilla products such as Mozilla Browser and email client.

Well, if Firefox will not open try safe mode. Safe Mode is a special way of running Firefox that temporarily disables extensions, themes and toolbar changes. If your problem stops while in this mode, we can find the item that is causing the trouble.