Don't build your own browser. Negotiate a deal with Mozilla foundation (and/or the other independent browsers) for a settings option that redirects account storage, password manager, etc. to Proton. Not a plugin and not a fork, but built-in and supported at Mozilla, so security updates happen asap. For this they deserve some support, and I'll be happy to see some of my visionary dues go there.
Don't build your own browser. Negotiate a deal with Mozilla foundation (and/or the other independent browsers) for a settings option that redirects account storage, password manager, etc. to Proton. Not a plugin and not a fork, but built-in and supported at Mozilla, so security updates happen asap. For this they deserve some support, and I'll be happy to see some of my visionary dues go there.