If you use Firefox or Iceweasel, you can disable most of those apis in about:config or user.js. For example, media.peerconnection.enabled = false, to disable WebRTC. dom.battery.enabled = false for battery, etc.

This would make absolute sense. Certain requests (like location) already trigger popups that ask you for permission. If it turns out other APIs can be equally revealing as far as privacy goes, it would make sense to present the same popup.

I mean, using a web app for the first time would be no different then installing a mobile app - I wouldn't be surprised if I had to give it a few permissions.

If you disable a unique combination of APIs that combination becomes your fingerprint.

By disabling specific APIs, you would make your browser even more identifiable.

It would only work if many users have disabled exactly the same APIs as you and all other non-disabled APIs don't provide any information useful for fingerprinting.

It's kind of surprising that there isn't an extension to provide this functionality (at least in desktop browsers). All you'd have to do is monkey patch the methods that get called and throw up a confirm("are you sure you want to allow [X]")

I don't know of any. I would think it would be fairly easy to create a userscript or extension to stub built-in APIs (maybe using something like testdouble.js or sinon.js to override the default global objects that you are trying to "disable"). I'm not sure what issues you'd run into on various pages if you did that though (so it'd probably need a lot of iteration- and fixing bug reports).

It might be a fun project to start though. I've been really enjoying testdouble's API (and have started using that for my unit tests).