Fingerprinting works by collecting bits of information about the browser and device to identify users. Couldn’t browsers 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.
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.
Sounds like you are talking about Firefox’s letterboxing feature which you can enable/disable independently from full fingerprinting resistance.