I agree with you about ads for sure. But I’m not really sure what you mean about https being off by default. What I’ve noticed is that if I type an IP address into the address bar, FF first tries https and if that fails falls back to http.
Regarding UA string: As a web developer I have worked on many projects, one currently, where browsers misbehave in unpredictable ways. Most notable these days is Safari. Without a user agent string I really don’t have a way to workaround that browser’s shortcomings. Yes, for this purpose, the UA string should be a last resort because feature detection is best, but trust me feature detection isn’t always possible. It would not work for the current slew of issues I’m working through in Safari.
Also, I would encourage you to read up on Brave and funder/fundamentalist Peter Thiel. Brave is not only a Google supporting browser by virtue of using chromium, it’s also wrapped up in some shady shit, including being funded by a conservative psychopath.