The problem

When starting Firefox (version 1.5), instead of the browser window, a window appears with the following error message:

"Firefox is already running but not responding. To open a new window, you must first exit the existing Firefox process or restart your computer."

But you are sure that Firefox is not running. Even a restart does not help.

The cause

Firefox was terminated improperly during the last session. This left a lock file in your home directory. Firefox then thinks that it is already running and does not want to restart.

The solution

Simply delete the lock file. The easiest way to do this is to use the following command, which removes the lock for all profiles at once:

user@linux> rm ~/.mozilla/firefox/*/.parentlock

Linux knowledge

These articles were written by the founder of Checkmk many years ago.
They are still valid though and thus we keep them on our website.
Mathias has since then developed a monitoring software called Checkmk

Find out more