Enable third party protocol handlers
As written in tor-browser#5556 (closed), there are good reasons for Tor Browser not to support magnet (or any other third party protocol handlers).
But, the threat probably doesn't always exist for most Mullvad Browser users.
There are roughly 4 cases:
- no proxy or VPN are in use in the system
- all connections are going through a VPN Tunnel
- the whole system is going through a VPN tunnel, except the browser
- no proxy or VPN are in use in the system, except the browser
- the whole system is going through a VPN tunnel, the browser is going through a different proxy
For case 1 and 2, there are no proxy/bypass or linkability concerns. (Which would be the big majority of Mullvad Browser users)
For cases 3, 4 and 5, the concerns are similar to Tor Browser.
So I think it would be ok to optionally enable external app links to open in apps. A good example of how it can be implemented is in Firefox Android, there is a preference called "Open links in apps", where you can chose between "Always" / "Ask before opening" / "Never".
We could offer similar choices.
(Then there is still the scheme flooding concern: https://bugzilla.mozilla.org/show_bug.cgi?id=1711084)