That's odd. You should only need one version installed, v121.0. Perhaps one version was installed OS-wide (in Program Files), and the other was installed only for the current user (in AppData)? If I were you, I would 1. make sure I didn't have anything of value stored in the older version (passwords, bookmarks, etc.), and export a copy if I did. 2. Just in case, I might make a backup from the new install of Firefox as well, just in case. 3. Then I would try uninstalling the old edition. 4. Once complete, I would check to see if the new edition was still functional. If not, a manual reinstall should fix that. 5. Lastly, I would import any bookmarks or passwords I exported in the previous steps, which I do not now have in my one functional install. I don't really store anything in my browser though, so this might be easier for me to do than you. Like I said, please make sure to export/back up anything you value in either/both, before uninstalling anything.