What's funny is that desktop versions of websites in a lot of cases are responsive, and work fine on small screen. BUT at the same time the mobile version is crappy and lacks some features (or just shows "download our app").
Recently I've set up Firefox on Android so that it always run in desktop mode. I needed to also change screen width in about:config, because otherwise everything is too small. But after this websites seem to work better.
quite likely that the site has a mobile "mode" and a small-screen mode (for desktop), each made by different teams. some mobile mode website is fine, but others suck. Where as the small-screen mode for desktop tend to be made by the same team/person as the main site (it's a css media query after all) - so it's likely to be more coherent.
Alternatively, you can download Firefox Nightly instead of regular.
"about:config" just works in Nightly. No fuss.
You can sideload extensions in Nightly, too, after you activate the developer options. I don't think they've added that to regular, as yet? At least not with as much flexibility.
Anyway, I'm gonna try this mobile desktop mode thing and see how it goes. Thank you to everyone!
Installing extensions from file is available on the release build as well, after enabling dev options.
I think the only difference is nightly allows installing unsigned extensions, which I don't personally have a need for (as getting a personal/non-published extension signed is very easy).
Recently I've set up Firefox on Android so that it always run in desktop mode. I needed to also change screen width in about:config, because otherwise everything is too small. But after this websites seem to work better.