I'd pay at least $10/month or $99/year for Firefox Accounts, just as they stand today, because they give me at least that much value. Integrate full 2FA into Lockwise, so that I have 2FA that'll never die with a broken phone, and I'd pay more. Add a secure calendar I can use with friends and family, and I'd pay more. (I'd hesitate to say email, just because running that is a can of worms I wouldn't wish on my worst enemy, but I'd absolutely pay for that too.) I would love to have all of my major services tied into my Firefox Account, with the same level of security, privacy, and trust I've come to expect.