No more user-agent, no reporting of available fonts, screen size, whatever. The browser needs to be a black box as seen from the server.
At the moment every browser on the web is just about uniquely identifiable. You can check this for yourself at the site of EFF: https://coveryourtracks.eff.org
This has to stop.
Zero-telemetry by default.
Support as many web standards/protocols.
Native UI controls on the host OS.