Just close that tab.
You don't really need to .. it has it's own backup system in .json anyhow .. and there are a load of them in the Profile folder.
http://kb.mozillazine...g_bookmarks_-_Firefox
Just delete what you need to on the toolbar .. bookmarks will still be there as they should have been copied from the bookmarks sidebar. You can L-click on, and drag into the sidebar if you need to.
As I said before, Help/restart without add-ons .. and select reset toolbars.