If you are looking for a specific type of result, like a bookmark or tag, you can speed up the process of finding it by typing in special characters after each search term in the address bar separated by spaces:

  • Add ^ to search for matches in your browsing history.
  • Add * to search for matches in your bookmarks.
  • Add + to search for matches in pages you’ve tagged.
  • Add % to search for matches in your currently open tabs.
  • Add ~ to search for matches in pages you’ve typed.
  • Add # to search for matches in page titles.
  • Add @ to search for matches in web addresses (URLs).
  • Add $ to search for matches in suggestions.

For example, if you’re looking for a page you bookmarked called Mozilla Firefox Support, you might type mozilla. The autocomplete results appear, but might not show the page you want.

You can narrow your results down to bookmarks only by making your search string mozilla *.

If you still have too many results, you can further restrict the search by making your search string mozilla * support #. Now the autocomplete list will only show bookmarked pages with mozilla and support in the page title.

Source: Awesome Bar - Search your Firefox bookmarks, history and tabs from the address bar - Firefox Help

I’ve been using Firefox for a very long time and just only now discovered these shortcuts. They appear to work on Firefox for Android as well.