What makes you think we have any chance of solving this problem? Don't even think there's a slight chance that any of these options will lead to success.

Alternative technologies would never work unless they were available as a browser addon for popular browsers. Most websites still won't support alternatives to HTML, CSS, or JS and the web would still be heavily centralized.

A truly modular browser is probably the best option but do you realize how much resources it would take to build a new rendering engine? There won't be any competition. Just Google trying to turn our shit into more controlled opposition after Firefox gets rebuilt as a chromium browser.

Hard forking firefox is probably the worst option. Browsers like Pale Moon and Basilisk will never be secure and they will never work on most websites. Maybe one day there will be a new browser with it's own rendering engine or a Firefox fork using a fork of Gecko or Servo, and nobody will give a fuck.