Sometimes a webpage works only on Chrome somehow. Would be fun if Firefox had some kind of extension to emulate Chrome for those scenarios.

Usually this is for one of the following reasons:

(1) negligence on the side of web devs (2) the site in silly ways relying on shit like google fonts or other trackers, which a privacy consciou user will block (3) the site relying on being able to plaster your face with ads, which u block (ha!) (4) stronger fingerprinting countermeasures on FF and again site stupidly relying on that (5) incapability of web devs to test their stuff properly (6) junior web devs being very green and not adhering to standards, that will work in any mainstream modern browser

In 99.9% of the cases it comes down to bad engineering or even intentionally ethically highly questionable methods.

For me it's Safari. In Firefox, everything works as I expect almost always. Chrome requires weird workarounds from time to time. And Safari is just all kinds of screwed up.