[email protected]: Do browsers block websites from uploading data that could be used for fingerprinting like resolution, installed fonts, etc.?

No, simply because even with pure CSS and even pure HTML you can find ways to leak some information about the browser. For example, a background image that only loads on 1920x1080, another for 2560x1440, and so on. Make hundreds of those for every possible resolution (they can be the same file on the server but at a different path), and there you go, you now figured that the client downloaded img/background/2448x1280.png from the server logs. You can use the same trick for fonts as well, you just apply the same trick on a box on the page that is sized based on text content. Repeat for every font you want to test for.

There's just a ton of those little features that are for performance optimizations because loading a 4K background on a 480p phone is a bad experience for everyone involved. Sometimes you need to know the size of some elements to position other elements relative to it. You need the mouse cursor position to open popups at the right place. You need the window size to realign popups and modals. You'd have to go back to text based only sites like it's the 80s and 90s to avoid that kind of fingerprinting.

And thus Tor's solution: everyone's got the same window size, same fonts and everything.

No, there is no way to prevent sites from uploading the info besides just not providing it in the first place.

And because of how programming languages work, there's no way for the browser to identify that data being uploaded "is" anything specific, especially when there's things like encryption, obfuscation or just re-arranging the data itself into larger collections of data.

Tor Browser does, but differently. It attempts to behave in the same way an all platforms, ignores installed libs/fonts/etc, uses letterboxing against resolution fingerprinting.

https://support.torproject.org/tbb/maximized-torbrowser-window/

LibreWolf can mitigate resolution tracking with an opt-in feature but it creates spacing around the windows so it's very inconvenient for many people. Idk any other browsers that do it.

Wtf@this dude's post history.