Whenever I browse the web using Mozilla (Google, Startpage or any other browser) AND Mozilla is set to fullscreen mode I get black bars all around website screen which are not present when Mozilla is set to windowed mode.

I am using: Macbook Air M1 (MacOS Monterey 12.6.6.) and latest Mozilla web browser. I have already tried this solution: "go to about:config in the address bar and try changing the value of full-screen-api.macos-native-full-screen to true" and it did not fix the issue. I am experiencing this for a lot of time now and only on my Macbook which means a specific version of Mozilla cannot be blamed. This happens on ALL websites. Note: I did change about:config quite a lot regarding privacy alterations.