To restore the Bookmarks of your Firefox after you have downgraded or upgraded it, please do the following:

  1. Click the menu button (  ) in the far top right corner.

  2. Click the question mark icon (  ) at the bottom to the right of the Customize option.

  3. Select Troubleshooting Information.

  4. Select Open Folder in the Application Basics list.

  5. Once the file is open, close your Firefox.

  6. Scroll down to find the "places.sqlite" file and right-click to delete it.

  7. Finally, open your Firefox and your Bookmarks should be restored.