Firefox is a web browser managed by the Mozilla Corporation.
 Unable to Launch Firefox
Sometimes, usually when Firefox is closed unexpectedly, the Firefox application will refuse to open, giving an error message similar to what is below:
"Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart the system"
In order to correct this issue, you must delete the .parentlock file and/or the lock file within your mozilla profile. This can easily be done with a few commands:
$ rm -rf ~/.mozilla/firefox/*.default/.parentlock $ rm -rf ~/.mozilla/firefox/*.default/lock
A small script has been written and placed on each server and lab machine to make executing these commands easier. From the command line, run the fixfirefox command, and the offending lock files will be deleted.
$ fixfirefox Firefox lock files removed. $
Afterwards you should be able to open Firefox like normal!