Interesting! Due to @Lioh 's video about mullvad-browser ( https://www.youtube.com/watch?v=vsB5FEq4rCA ) I learned about 'letterboxing' in firefox. Letterboxing creates a spaces around the actually displayed contents in the browser windows that won't be used then - this helps a bit against browser fingerprinting. This is available in librewolf AND in firefox, too. In librewolf the config key

privacy.resistFingerprinting.letterboxing

exists and is set to false per default -

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