Usually this message indicates that the last updater failed to replace all of the files in the program folder, leaving a mix of some newer and some older files. The remedy is to run the full installer again but actually I'm puzzled that after you get the message, you can still run Firefox. ?? As a precaution, you certainly can make a backup of your bookmarks. I suggest using both formats, and saving the file somewhere that Firefox doesn't "clean up", such as your Documents folder. (1) JSON format backup file: [[Restore bookmarks from backup or move them to another computer]] (2) HTML format export file: [[Export Firefox bookmarks to an HTML file to back up or transfer bookmarks]] (You also can back up your entire profile folder: [[Back up and restore information in Firefox profiles]]) And then you can get a fresh Firefox 133.0.3 installer at https://www.mozilla.org/firefox/all/desktop-release/ That installer should detect your existing data and do an in-place upgrade.