That sounds great! I actually made something very similar to this (a middle man to set as my default browser), but for some reason it was incredibly slow to open specific Firefox profiles. I’ll take a look at how you implemented yours :)
In Tauri, registering your app as a handler for a URL schema is very easy, all of the hard work is already done at https://v2.tauri.app/plugin/deep-linking/ haha. If you haven't played with it, I highly recommend it. It's really nice.
Oh, and for web protocols specifically, I also have to prompt the user to register as the default browser for security reasons, but that's about it. Sorry for ruining the magic :D