When logged in to a Linux lab machine or compute server, you may get the following error when opening Firefox:
“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.”
This may occur even though no evidence of Firefox running can be found.
To remedy this, open a Terminal and run the command: foxlock
It’s a script we wrote that will remove the necessary files from your .mozilla folder and allow you to open Firefox once again.