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.
It absolutely, positively is on by default. Moreover, it’s actually quite hard to completely turn off. Even their new fancy switches are sus, but for the longest time you needed to go to about:config and switch like ten different weirdly named parameters to turn everything off.
Weird. I was just setting up three Linux laptops and was asked if I wanted to turn these features on every time.