One of the very annoying consequences of the Chromium move to snap on 20.04 is that it will silently fail to launch most external links (e.g. Slack, Zoom).
It basically breaks xdg-open. This is crucial for a lot of flows with desktop software and I'm honestly baffled why it isn't fixed. Any URI with a custom scheme is horribly and completely broken with a browser installed as a snap. Even basic stuff like file uris are broken in browsers installed as a snap.
It's extremely weird to see this kind of thing when it happens too, you usually trust Firefox to work!
A workound is posted at https://bugs.launchpad.net/snapd/+bug/1776873/comments/29 (simple patch & recompile). May be worth making a PPA for the fixed snapd if we can't get the Canonical dev team to fix the core issue.