You can simply uninstall the older version, and Firefox will continue to work normally. sometimes this happens, I'm not 100% certain as to the cause, but there's no harm in removing the old version.

Ok, So just to be clear, it won't uninstall version 64 or delete all of my favourites if i uninstall the old version (57) ? Because the last thing that i want happening is that i lose all of my favourites (and i have a lot of them). P.S. Did you see the screenshot because i wasn't sure whether it uploaded correctly ?

Firefox comes in two or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

If both version are 32-bit or 64-bit Firefox versions then uninstalling the other Firefox version will likely remove the other version as well because both registry entries point to the same folder. This can happen if the Firefox updater didn't remove the entry of the previous Firefox version, but merely added a new entry for the new release. If the two Firefox versions are installed if separate Firefox program folders then you ca safely uninstall the older Firefox version. If you would uninstall both Firefox versions then you can just reinstall Firefox.

• https://www.mozilla.org/en-US/firefox/all/

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.