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.
I don’t think that Sneaky or Secret are good descriptions for this. A better word might be “plumbing”.
When you realize that your house use full of hidden pipes and wires, it would be a strange take indeed to conclude that anybody is being “sneaky” about these “secret” features.