I have noticed recently I can no longer delete single entries in the autofill drop down. Currently using a MacBook Pro. Ive tried all the suggestions listed and tried Firefox in Safe Mode with no luck. I use the down arrow to highlight the entry and when I use Shift+Delete, the drop down list disappears. Ive tried just highlighting and using only the Delete key and that does not work either. Ive restarted my laptop as well, just in case, and still have no luck.