How to fix “Firefox is already running” error on Linux

How to fix “Firefox is already running” error

Sometimes when I try to start Firefox, it warns me that Firefox is already running. The message looks like this:

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

Usually, you can just kill the firefox process to solve this problem. For example, on Linux the command “ps auxwww | grep firefox” will find the process number and then “kill [processnumber]” will work fine. 

If none of that worked, try killall [processname]. Example to kill Firefox

killall firefox.