The address bar in Firefox is intelligent and shows many results in a dropdown as you type in the search term, page title or URL you are seeking. These results dynamically adapt as you type in more of your text in the address bar. There are special characters that you can type in the Firefox address bar to narrow down the dropdown results:
*: Only show matches from your bookmarks.
^: Only show matches from your browsing history.
#: Only show matches in page titles.
$: Only show matches in page URLs.
?: Remove everything (pages from history or bookmarks) but the search term suggestions.
As an example, I would type
merge sort ^ in the address bar to restrict the dropdown results to only matches from my bookmarks. These characters can also be combined to further narrow down the results, though I have never had to do that.
Reference: Address bar autocomplete in Firefox
Tried with: Firefox 71.0 and Windows 10 x64