Firefox’s free VPN will offer 50 gigabytes of monthly data, which is pretty generous for a browser-based VPN. A Mozilla account is required to make use of it, which isn’t a hardship (they’re free), but is a point of friction some may wish to know upfront.
Another server that belongs to the same company as your browser, so they have an access to both ends of the direct line. If you don’t trust Mozilla to be thrustworthy vpn server (which is good, shouldn’t trust anyone), bad news, they already have an access to your whole traffic because they own your browser