Could you make an extra copy of your bookmarkbackups folder in some safe location? To access that folder, use Help > Troubleshooting Information > "Show Folder" button You can use the .json files in this folder to restore previous day's versions of bookmarks if other approaches don't work. ---- If you open the Properties for one of the bookmarks that has this problem (on Windows, it's on the right-click context menu), can you see a change to the Location as well as the Name? The Location normally has the URL. ---- Do you use Firefox Sync? If so, what other programs/devices do you sync and have you noticed any odd issues on those as well?