If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix: *bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx You can find the IDs of the submitted crash reports on the <i>about:crashes</i> page. *You can open the <b>about:crashes</b> page via the location bar, like you open a website, or open the crash reports page via "Help > Troubleshooting Information". See: *http://kb.mozillazine.org/Mozilla_Crash_Reporter *https://support.mozilla.org/kb/Mozilla+Crash+Reporter See also: *http://kb.mozillazine.org/Firefox_crashes *https://support.mozilla.org/kb/Firefox+crashes ----- Your System Details list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file is only present if you or other software has created this file and normally it wouldn't be there. You can check its content with a plain text editor (right-click: Open with) if you didn't create this file yourself. The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session. You can delete the user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release. You can use this button to go to the currently used Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) See also: *http://kb.mozillazine.org/Preferences_not_saved