"Facebook.com" is a built in suggestion to firefox that I cannot seem to remove. I've disabled every form of suggestions and tried 'shift + delete' as suggested here.
I do go to facebook.com/marketplace and I'd love for THAT to autofill from history. I have cleared all history, clicked 'forget about this site' from the history page, you name it. It seems impossible for marketplace to autofill instead of facebook.com
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.
There are a couple somewhat similar ideas here in the community:
Add an option to remove sites from search
Or you can update your search preferences:
That should put history & bookmarks ahead of search suggestions.
If that doesn't work, let us know.