Entries in the location bar drop down list with a yellow (blue on Mac) star at the right end are bookmarks.
You can remove such a bookmarked item that shows in the list if you open that url in a tab and click the yellow star in the location bar.
This will open the "Edit This Bookmark" dialog and you can click the Remove button to remove the bookmark if you want to remove such a bookmarked entry.

• Remove websites from the address bar suggestions
• Cannot clear Location bar history

I want to delete history from my address bar permanently. I’ve tried this thru tool and they always are still there. When I type in a letter the sites I have visited pop back up. Is there any way to get them gone for good? This is not a book mark, but rather the first initial of what I put in the address bar gives me the drop down menu I want to delete.

A possible cause is a problem with the file places.sqlite that stores the bookmarks and the history.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox