[roca]

Mozilla put in a lot of effort to let you run your own Firefox Accounts server if you really want to. https://mozilla-services.readthedocs.io/en/latest/howtos/run...

So pretty much the opposite of what you're afraid of.

[cdubzzz]

Looks like this has improved a lot since I used it a few years ago. That documentation even seems a bit outdated -- the new monorepo is here: https://github.com/mozilla/fxa.

I eventually abandoned it when I was cutting back on things I had to manage, but maybe I'll take another look soon...