What is the perceived problem, then?

Make sure to read this thoroughly this time.

[...]it's almost always a manufactured limitation.

Doesn't that sound like a good description of a problem?

I think I've only ever encountered a single website that didn't actually technically work on Firefox[...]

There's gonna be a hell of a lot more of them, buddy. You're gonna have to hang your cat on your balcony to get an estimate of future weather if you want to avoid using one of them how-are-these-even browsers.

Imagine yourself as a homosexual man in Iran (should be easy). Would you say that hiding that big part of you from everyone and even go as far as marrying a woman you don't even like just not to arouse suspicion makes the problem disappear? Just the fact that you need to spoof your useragent to view a shitty website, the developer of which would (should) die under a car one day 🤞, is a solid proof that you will soon be that homosexual man in Iran.