I don't have Top Sites in my bookmarks bar but I can make a suggestion if the above doesn't help: Go to Bookmarks > Edit Bookmarks. You may be able to find Top Sites there. If so, you should be able to delete it by selecting it and pressing Delete.
The contents of Top Sites are listed under Favorites on the Bookmarks menu.
If we knew what it was we were doing, it wouldn't be called research, would it?
