There is a common error documented in https://support.mozilla.org/en-US/kb/firefox-already-running-not-responding but none of the solutions fix my problem. I have signed out of my PC and mobile devices Done a complete uninstall of firefox on the Windows 11 machine Searched and removed ALL files on the drive associated with Firefox or Mozilla, including cache and temp Searched and removed ALL Firefox or Mozilla keys in the registry Checkdisk Used update to refresh the windows install Multiple reboots and a fresh download and install of Firefox. And still get the "already running" error. If I wait long enough - several minutes - I will get the "crash report" screen as the background process finally ends. Any suggestions?