If those bookmarks are in the toolbar in FireFox - choose Show All Bookmarks, and edit the bookmarks toolbar from there. You can delete any bookmarks, edit the existing ones, move them around, etc.
If you only want to delete a single bookmark, you can click on the blue star in the location windows, which will bring up a delete menu.
There's also other methods. Search through your FireFox help for 'managing bookmarks' and you'll see other choices.
In Firefox open, view> toolbars> customize.Bottom left hand corner you will see a box that allows you to display favicons with text,or text only or reduce size of toolbar. That should take care of your problem !