Firefox Will Not Load

Scenario: Firefox complains that there is another instance of Firefox running.

First, make sure you really don't have another Firefox running on some other machine on the net.

Then, in your home directory...

cd .mozilla/firefox/
cat profiles.ini

Look for your default profile name (which has a random string of characters and most likely has .default attached to it.) Some people have multiple firefox profiles. Most people have only one. Run the ls command to make sure you have that same profile directory as listed in profiles.ini.

Then...

cd profile-directory

You should now be in a directory now that looks something like this:

.mozilla/firefox/jhjid5mz.default

NOTE: Your profile will have different characters in the profile name than what you see directly above.
ls -al

Look for a file called lock.

Normally, the lock file would have been automatically removed when Firefox last exited, but sometimes it does not get removed. So, we're going to have to remove it by hand.

Also, sometimes there is another file leftover called .parentlock (notice the dot before "parentlock"). That file will also have to be removed by hand.

Therefore, remove the lock and .parentlock (if one exists) files from your profile's directory.

rm lock
rm .parentlock

Restart Firefox, and this time, Firefox should load correctly.

You can also check out the following webpage that discusses the same issue:

http://superuser.com/questions/78917/ubuntu-firefox-it-is-saying-that-it-is-already-running-but-not-responding