Visit about:compat in your firefox. I find it insane that these exist.
Edit: I’ve learned that this is part of the webcompat system addon developed by Mozilla and other contributors. I see why this is beneficial default behavior, since FF has no chance of getting enough market share to matter more if things are broken.
However, this behavior is too intrusive for my taste. For example this injection: https://hg.mozilla.org/mozilla-central/file/8a4afb4d34f8/browser/extensions/webcompat/injections/js/bug1472075-bankofamerica.com-ua-change.js is basically just to silence annoying user reports.
Also, Every site FF pretends to be a different UA on is artificially reducing FF market share data.
… Uh… This doesn’t seem that objectionable. It’s a bunch of targeted fixes to websites, I imagine every browser does it in some form. Firefox at least allows you to turn it off if for some reason you wanted to.
BTW, I think Proton (for playing games) does this as well.
Ehhh… I think a bigger effect on FF market share statistics is probably all those privacy addons and settings everyone is using.
Windows does this as well. No doubt the same for macOS.