To refresh Firefox back to its default settings, go to Troubleshooting Information.
  • Type about:support into the Firefox address bar.
  • To the right, click the Refresh Firefox… button under Give Firefox a tune up.
  • A Refresh Firefox dialog will display with information about what will happen if you proceed. Click the Refresh Firefox button to continue.
  • Firefox will close while it refreshes, and then relaunch. When Firefox relaunches, you will have the option to Restore all Windows and Tabs, or Restore only the ones you want.