When you open Firefox in Safe Mode, it automatically disables your custom settings, themes, and add-ons. THOSE changes are temporary. However, if you click any of the boxes underneath the line, "You can make some or all of these changes permanent", and then choose "Make Changes and Restart", everything you checked will be forever changed, even when you start Firefox again in 'normal' mode. [See attached image for a preview of the Safe Mode options]. To be clear: 1. If you check any of the boxes but do NOT select "Make changes and restart", those things will not be changed at all in safe mode. 2. If you select any of the boxes and you DO select "Make changes and restart", you will permanently lose any of the items you checked (bookmarks (except for backups), user preferences, etc.). If you performed the action in step 2 above, you will only be able to restore those things if you have a previously created back-up of your Mozilla Profiles folder (not the same as the Firefox program folder). Hope this helps.