“#Mozilla is scheduled to add a new user anti-fingerprinting technique to Firefox version 67, scheduled for mid-May.
Called "letterboxing," this new technique adds "gray spaces" to the sides of a web page when the user resizes the browser window, which are then gradually removed after the window resize operation has finished.
Letterboxing was originally developed for the #Tor Browser four years ago, in January 2015.”
“Letterboxing is currently available in #Firefox Nightly.
The feature isn't enabled by default, though. Firefox users will first need to visit the about:config page, enter "privacy.resistFingerprinting" in the search box, and toggle the browser's anti-fingerprinting features to "true."”