If you can't delete them in the normal way in the Bookmarks Manager then you may have a problem with the file places.sqlite. See http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox

See also Deleting bookmarks

I have the same problem. Although I'm able to remove them by right-clicking, clicking Customize, and then just dragging them out. There are quite a few of them. They just keep generating and I don't want them to? What's the solution?

I just uninstalled and reinstalled-problem solved (I transferred my bookmarks and settings to IE and transferred them back)

Thanks! That worked!!!