Resetting preferences (zoom, tabs, privacy, network, encryption, updates, where to save file downloads, etc.) is one of many procedures that can be helpful in troubleshooting Firefox problems. We'll explain two ways to do this.

• If changes to preference settings are not saved when you restart Firefox, see How to fix preferences that won't save.

Solution 1: Refresh Firefox

The refresh feature restores Firefox to its default state while saving your essential information. This solution will reset preferences but will also remove other customizations, including added extensions and themes. For more information, see Refresh Firefox - reset add-ons and settings.

Solution 2: Delete Firefox preference files

1. • Click the menu button , click Help and select Troubleshooting InformationMore Troubleshooting Information.From the Help menu, select Troubleshooting InformationMore Troubleshooting Information. The Troubleshooting Information tab will open.
   • Under the Application Basics section next to Profile FolderDirectory, click Open FolderShow in FinderOpen Directory. A window will open that contains your profile folder.Your profile folder will open.
   Note: If you are unable to open or use Firefox, follow the instructions in Finding your profile without opening Firefox.
2. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit.
3. Locate and delete the file prefs.js (or rename it, for example, to prefs.jsOLD, to keep the old file as a backup). If you find more than one, a prefs.js.moztmp file or a user.js file, delete (or rename) these as well.
4. You can close the profile folder and open Firefox now.