This is an open issue on the Mullvad Browser GitHub.
One person in the thread who's using Pop OS posted this:
xdg-settings set default-web-browser start-mullvad-browser.desktop
However they do report the clicked URL not being passed to the browser, so it doesn't seem to be that good of a solution.
This reply worked for someone on Arch though.
I'm having the same issue, so I will try to fix it later and get back to this post if any of these methods work.
EDIT: I tried both methods. The Arch one did nothing, while the xdg-settings one did set Mullvad Browser as my default, but when I click a link the browser will open on the homepage anyways. So yeah, seems like we gotta wait for this to get fixed by the Mullvad devs.
I had tried that but Network Manager couldn't read the config or something. Anyways I fixed the issue by enabling quantum tunnel, but thank you anyways for replying!
@nxnx
@lemmy.blahaj.zone