

The VPN that Mozilla (Firefox) has sold for years was rebranded Mullvad. Assuming they’ll still use Mullvad for this, I wouldn’t worry.
EDIT: I’ve since seen somewhere else that Mozilla may not be using Mullvad for this, just to clear for anyone reading this later.
The VPN that Mozilla (Firefox) has sold for years was rebranded Mullvad. So, as long as they’re still partnering with Mullvad for this, I think logs are impossible, as Mullvad traffic all runs through RAM and that’s been tested and proven.
EDIT: I’ve since seen somewhere else that Mozilla may not be using Mullvad for this (just to be clear for anyone reading this later).