see the attached pic

Looks like some Unicode bookmarks that have their titles shown as the combining (western/windows) characters. If you can't remove them via the right-click context menu and in the Bookmarks Manager (Library) and sidebar then it possible that places.sqlite that stores bookmarks and history is corrupted. Note that removing places.sqlite will remove all history. ---- If you use Sync then best is to disconnect Sync temporarily during troubleshooting. You can check for problems with the <b>places.sqlite</b> database (bookmarks and history) in the Firefox profile folder. *use "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page See also: *http://kb.mozillazine.org/Locked_or_damaged_places.sqlite *https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file If "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page cannot repair places.sqlite then remove all places.sqlite files in the Firefox profile folder. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder. *keep a backup copy of places.sqlite in case a new places.sqlite database has to be created *http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page. *Help -> Troubleshooting Information -> Profile Directory:<br>Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder *http://kb.mozillazine.org/Profile_folder_-_Firefox