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.
If they are having to add compat, it is because it is a popular site that is already ignoring Firefox. I am sure they have communicated the problems. The website operators don’t care.
What hurts Firefox market share is when regular users have problems on the sites they frequent. The lower Firefox market share, the fewer sites care about it ( as you seem to understand ). Firefox has to make these kinds of fixes.