Firefox has a lot of issues, but maybe we don't have any other option.

No, it's not intermittent; it's useragent specific. There are a lot of websites that will work fine in Chrome or Edge, won't work properly in Firefox, but will work properly in Firefox when you lie and say you're running Chrome

I mean is it so difficult to understand? That's not meant in an insulting way, but maybe I'm considering the point to be more obvious than it is depending on perspective (so the problem is me, I mean).

Ultimately, this always comes up, and then there's so many related points. "Firefox keeps being made worse", "Wow look how Chrome owns everything and Google forces it down everyone's throat", "Look how MS pushes Edge", and they all have in common that they seemingly misunderstand how people - excluding a niche like those over here - utilize their web browser.

That is, they don't. Do you honestly think about the brand and the specifics of your hammer every time you hammer in a nail? You don't. It has a specific used: To hammer in a nail. Does it do that? Cool! Is it perfect? You don't actually notice, because your mind was on putting in a nail, not admiring the hammer, customizing it, or complaining about how the serial number is written the wrong way. Not only do these problems never cross your mind, evaluating the problem presence never crosses your mind: You could not realize the problem in the first place, as your context for the action never establishes a perspective where the hammer in itself could even have problems of its own.

Or to loop it back around to browsers: A browser is not a concept that most users actively create in their mind. In particular not when browsing to web pages. They tap that icon, but only because it is the action needed to create the outcome. All further points are not only irrelevant, they're not points in the first place. They cannot be. The context does not have space for points about the browser.

And it's this inability to grasp the not only invisibility but also sheer mental inexistance of browsers as a category of software in most users that very many hardcore users and privacy nuts seemingly struggle with. Which makes sense. We cannot not think about it. But likewise, everyone else cannot think about it. And that second group is orders of magnitude bigger. And they use whatever their system ships with, because that's how their phone or laptop, well, works. Sometimes you buy a device where the icon for accessing web content is different. Yeah. Doesn't matter, tap it or click it.

That's not me selling users for stupid, either, another sentiment I see a lot. They are trying to put in a nail, and their actual problem is locked behind that. They are trying to solve a problem, and their brain has neither space for points about their browser, not for points about the concept of a browser as a whole. Because what they need that tool for is in itself just a secondary step in trying to solve an actual problem. Say, looking up whether it was 300g or 500g of flour for the recipe they're half-remembering.