Firefox ESR 60.0.2 Background: Firefox running on terminal server - with multiple users connecting GPO in place to restrict access to C: Firefox installed on C: users profiles are stored on a network share (including App data) Issue: Every time Firefox is launched either (cyclically, the user sees a message that there was an error restoring the last session, or an error message "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." is displayed." Tried: re-installing Firefox deleting parent.lock starting with addons disabled My thoughts are that this is either to do with the App data profile stored on a network share, or that the local install is on C: which is no longer accessable for the users (however application is still able to launch, and no other local applicaitons are effected.).