When quitting firefox and starting it again shortly after (while the old process is still busy with cleanup? wtf?), sometimes a dialog box appears, with the following text: "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 is bad advice. A user process should not ask for a restart of the system.
This message will be displayed when your Mozilla profile is locked. This can have multiple reasons. So this is a *generic* message and Mozilla is recommending a restart as final hint because not everyone is able to bring up task manager or inspect running processes to determine and kill dead/blocking Firefox. I.e. the typical "Have you tried turning it off and on again" approach which is funny for skilled users but working for non-technical users. We are not going to patch this message in Gentoo. Please talk with upstream if you care.
