> what browser am I supposed to use from now on?
There's actually quite a few. This Wikipedia list [0] might not be the best curation, but it carries my point, somewhat. For example, I've really enjoyed the power-user browsers, like surf, luakit or uzbl.
I know you were expressing the fact that we're stuck between Firefox and Chromium, because they're the only browsers able to keep up with the rapidly moving web stack and provide a fluid user experience at the same time. My point is if you're willing to compromise on that, you actually have other choices.
Oh I do hope to see the day when there's a variety of browsers, all equally compatible with the day's web. Doesn't seem like we're moving in that direction though.
Personally, I tolerate Firefox, because I want some of the extensions, namely Dark Reader and ublock. Dark Reader doesn't really have alternatives, as far as I know, and I find that network level blocking isn't effective or ergonomic enough to replace something like ublock origin. If I solved these two problems, I'd jump ship to surf immediately.
Just to finish my rant; the other day I was experimenting with text browsers for rendering simple sites like thefreedictionary or HN. Their ability to do that is quite abysmal. I think that says a bit about the state of web's accessibility.
[0] https://en.wikipedia.org/wiki/List_of_web_browsers