I'm not sure it makes sense to start a new thread to direct attention to a different thread. You could consider creating a new Firefox profile. This would work around the possibility of a corrupted history (places.sqlite) file. You can import your bookmarks to the new profile and then test whether it has the same shutdown problem. First, I recommend backing up your Firefox settings in case something goes wrong. See [https://support.mozilla.com/en-US/kb/Backing+up+your+information Backing up your information]. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.) Next, with Firefox closed, fire up the Profile Manager to create a new profile: [http://support.mozilla.com/kb/Managing+profiles Managing profiles]. To move key settings like bookmarks from your damaged profile to the new profile, see: [https://support.mozilla.com/en-US/kb/Recovering+important+data+from+an+old+profile Recovering important data from an old profile]. Does that shut down cleanly? As you recustomize and install add-ons, you may find the cause of the old problem, or it might never recur. To be determined.