I follow the procedure, click on Remove Bookmark. Click on Bookmarks again and it is still there.
Go to Solution.
Many thanks, that fixed it!
You can check for problems with the places.sqlite database file in the Firefox Profile Folder.
I had same problem for about 3 weeks before I clean installed FFox 19.0 (after 18.02) had a lot of issues when I imported HTML backup.
Only today I discovered using the "Bookmarks Sidebar" to delete items and including item separators.
FFox MenuBar > View > Sidebar > Bookmarks
Right click on unwanted items > Delete
I hope this works for you