It isn’t an exact match to what you have claimed, but if it was going to start happening I’d expect it to have started by now. But for example, my favorite sites works fine in Lynx, let alone old versions of Firefox.
I really don’t get it. It isn’t obvious to me if people are really experiencing compatibility issues, or if it is just a boogeyman…
In many cases, you are not experiencing compatibility issues precisely because Firefox is still being actively maintained.
For new web technologies, the consequences of Firefox not supporting them is obvious. But even for existing sites, Mozilla is maintaining a long list of "Web Compatibility" patches that can be updated outside of regular browser updates (which is important for long-term support versions and managed environments): https://hacks.mozilla.org/2019/07/firefox-68-bigints-contras...
That's exactly the type of thankless but essential work that I fear people are always underestimating when talking about "just developing a new web engine". It's probably difficult but still feasible to become "standards complete"; becoming and remaining compatible with HTML/JS as it's actually written in the real world seems much harder.
It isn’t an exact match to what you have claimed, but if it was going to start happening I’d expect it to have started by now. But for example, my favorite sites works fine in Lynx, let alone old versions of Firefox.
I really don’t get it. It isn’t obvious to me if people are really experiencing compatibility issues, or if it is just a boogeyman…