Cheers Sam. I don't know much about protocol handlers, but one that you use quite often, apart from https:, is the mailto: handler. Type that into your browser and it might open your email program.
You can also use your browser as a file explorer by using c:, spotify: also works for me, as does ms-calculator:, and if you're a bit nerdy, javascript:.
You can make these into bookmarks too if you wish.