Essentially all of Firefox' incompatibilities with a website reduce to Firefox not allowing the users to be tracked or fingerprinted by default. Webapps that rely on fingerprinting as a replacement for device tokens will likely not work. Because fingerprinting is bad and I don't want it to work. The people your bank pays to implement that are the same companies used for cross site tracking. It only works because tracking works. ReCaptcha can break for similar reasons, but there are better options for captcha and the need for captcha itself is possible to eliminate with various strategies depending on what it is being used to mitigate.

There's a lot of good use-cases of Web usb, you can't just cut everything which might have privacy aspects otherwise the browsers wouldn't have canvas or even gpu rendering.