By default, Firefox suggests items from both your browsing history and your bookmarks when you start typing in the address bar. If you've cleared your browsing history then, obviously, Firefox can't look there for suggestions but you ought to have AB (and any other regularly used websites) bookmarked. That means that
(a) you'll be able to access them from the Bookmarks menu ; and
(b) you'll be offered those addresses as soon as you start typing in the address bar.
If you're not bookmarking your regularly used websites then you're not using Firefox efficiently. (I've got thousands of bookmarks). To bookmark a site, simply press Ctrl and D together. (To view your bookmarks, press Ctrl and B together and then click on Bookmarks Menu. Or, if you've got the menu bar [File/Edit/View/etc] across the top of your screen, simply click on Bookmarks).
Even better though, put all of your most popular sites onto the Bookmarks Toolbar at the top of your screen. Here's what mine looks like:
http://upl.co/uploads/Toolbar1517511919.jpg
It's dead easy to do that. Simply right-click near to the top of your screen and check that there's a tick next to Bookmarks Toolbar. (If there isn't then, obviously, put one there). Then, when you're viewing a page that you want to have available in just one click, drag the little 'i' in a circle (to the left of the address bar) onto the Bookmarks Toolbar. Job done! (If you'd rather have a shorter, or different, name for what you see, simply right-click on it, select Properties and change what's in the Name field)