For a long time I've used Firefox on Linux with multiple instances each with their own profile folder. Today when I try to run these instances with separate profile folders I get the following error: > Firefox is already running, but is not responding. To use Firefox, you must first close the existing Firefox process, restart your device, or use a different profile. Profiles are created like this: firefox --new-instance --createprofile "PROFILENAME ~/.firefox-PROFILENAME" They are run like this: firefox --new-instance --profile "~/.firefox-PROFILENAME" It seems something has broken with the instance isolation as this is now throwing an error. Additionally I run "createprofile" it doesn't seem to actually create the folder.