Actually, they rather lost a lot over the last years, with various shady things, like tracking for advertisement enabled from the browser by default (called studys).
So sadly, I also would not trust them as a VPN. Way more than some random VPN service, sure, but not completely. But I also do not know of a better alternative.
I've lost track of the times a Mozilla misstep has resulted in people here saying that's the reason they're switching back to chrome, which I find frankly ridiculous. Also, the whole damn thing is open source, so it's not like they're really hiding anything, people just don't care until someone makes a stink and then all of a sudden everyone cares a lot.
No browser is perfect, but Mozilla is definitely one of the better ones for anyone privacy conscious.
We technical folks get it and can deactivate it.
Every non technical person I know, who still uses firefox does not know and has all the defaults activated, until I change it for them.
So sure, they are still better than google and microsoft, where I just assume that they track everything, but that is a really low standard.
Some of the other incidents were overblown but the Cliqz thing shows of a company culture where user data is something which can be sold to make a profit, which is essentially what they did, and not something which is vital to protect.
Yes, it was many years ago now but I have no reason to think that they cleaned up their company culture.
All Mozilla know is the mullvad username. Mullvad don’t know the credit card details of the purchaser. To link a given vpn ip to a specific credit card would require compromising mullvad and Mozilla.
(Or of course the normal way of fingerprinting which doesn’t rely on IPs)
Now sure you can buy mullvad via cash, but that’s far more work. Using Mozilla as a reseller feels like one more step in the chain