Isn't the Firefox VPN just a rebrand of Mullvad or something? Like they just use their servers and put in their logo?
I have been using PIA for the last few years and I am personally pretty happy. I had some issues with Nord connect and speed a few years back. PIA on wireguard has worked great for me. I have a gigabit connection and although I can't hit that with pia, my Unraid SabNZB hits over 70MB/s easy which is great