Help making firefox 1920x1080 again

[zyn23]

I can't make firefox go back to fullscreen (as in no letterboxing and 1920x1080 resolution), I already changed this settings in user.js but nothing seems to make a difference
user_pref("privacy.window.maxInnerHeight", 1080); user_pref("privacy.window.maxInnerWidth", 1920); user_pref("privacy.resistFingerprinting.letterboxing", false);