For example I use Opera to browse `facebook.com/messages`. It's a bad UX for writing (somehow it "swallows" some of the written text when you type too fast, or select text and try to overwrite it), but this makes me use it less. Won't ever install FB app on my phone.
I was literally using it fine one day, then the next they started saying I need to use the desktop website for menu editing as it's "more optimized."
Dinguses, if I'm manually turning on Desktop Mode I know it's not gonna be "optimized." Just let me get my menu edits pushed goddamnit!
Especially if viewport scaling is disabled.
People with vision impairments need to be able to zoom.
Surely you don't mean to block our popups, right?
Surely you didn't mean to block our auto-playing video, right?
Surely you would rather use our lousy app rather than the desktop web site you explicitly requested, right?
etc.
Also Wikipedia. I don't remember if I particularly disliked the first-party app, but I vastly prefer Wikipedia in a web browser.
It's 13:41 on Tuesday, October 14 - Don't forget to give us money!
If you want full fooling, install a UA changer on your Firefox mobile, and you're laughing.
Apple has started down this road. All iPads now use desktop user agents.
The browser vendors already do. What do you want to change?
Firefox on Android seems pretty good on desktop-mode, though: its resolution seems desktop-like, and sites rarely give me the mobile treatment.