Proton is the end of a long-overdue overhaul of the UI to fit with the modular, quicker backend, if I understand it correctly. The addon API was more painful but similar. Both should have happened a long time ago, and would have saved countless developer time spent on the old codebase.

They could have done it all at once with a full experimental browser again, which is what Phoenix originally was. But that doesn't fit with the branding and telemetry obsession Mozilla has.

It's not as bad as they make it out.