As other people are saying, I think you can cut out one of the accounts browsers and just login to everything on one browser and keep Mullvad for random searches, particularly if even the sensitive accounts are still your “main” identity, if that makes sense. The one exception I can think of would be if you’re a journalist or whistleblower of some sort, at which point I would recommend confining those activities to a different device entirely.
I use a similar setup, Mullvad is my default browser for opening links and random searches, whereas Firefox is where I do my email, banking, shopping etc.
On mobile I use Firefox Focus for random searches and IronFox for accounts and PWAs. I wish the adblocking on Focus was a bit better, though, or if they allowed you to install Ublock Origin… If Mullvad browser released on Android I’d be overjoyed.
Didn’t know about this, seems interesting,