

I wouldn't be too offended if browsers changed the way they handle schemes: always open a "how would you like to handle this link" dialog for any protocol (even if unhandled - like how Windows shows the "how would you like to open this file" dialog), to disguise whether the protocol is handled or not.

I've actually never checked the "Always open Slack for slack:// links" or similar checkboxes, precisely out of predicting shenanigans like this would happen eventually :) I'll probably be more inconvenienced by the mitigations that will surely result that make it that much more painful to actually launch a URL scheme, sadly. So it's cute, but not practical, and I won't lose sleep over it. It's clever but somewhat obvious (in both a to-the-user-that-its-happening and a "well of course it's possible" sense). I'm going to close a website as soon as I get an unprompted popup that says "Firefox is trying to open Slack."
