I'm running Arch btw, with GNOME Shell 3.38.3 and Firefox 86.0 (64-bit). If I have Firefox already open and I click on a link inside of another app, Firefox displays the following error message and the link fails to open. 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. However, if I close Firefox and then click the link again, Firefox will correctly open the link.