firefox' address bar autocompletion recognizes special chars for filtering suggestions:

% - search open tabs
^ - search history
* - search bookmarks
+ - tagged bookmarks
$ - filter suggestions by url
# - filter suggestions by title/tag

firefox browsing hotkeys autosuggestion opensource

wife pointed out that if you click on the location bar, where it pops up the suggestions. you can see the character for the suggestion type by hovering over the corresponding icon next to the "This time, search with:" textbox.