Fingerprinting works by collecting bits of information about the browser and device to identify users. Couldn’t browsers like Firefox see when a website gets such info with JS and either prevent or ask permission from the user for the website to make HTTP requests to upload such information to the website. Idk if they do something like this already.
Yes, Firefox already provides some protection against fingerprinting.
I’m not sure if resistFingerprinting does anything to stop websites from uploading whatever data they can get though, I don’t think it does that. And I don’t think it could really do that in the first place since the website could just obfuscate the data and browser wouldn’t know what is sent.
No defense is perfect, of course. To prevent client-side code from running, you can always install NoScript.
Privacy is an endless treadmill, though; they are always finding new ways to get around protection. You may get a good level or privacy with the right tools, but it will also be super inconvenient.