Firefox Fullscreen Transition (Fade) & The Warning

TL;DR Go to about:config, look for these settings and change their values. To remove the fullscreen fading: full-screen-api.transition-duration.enter => 0 0 full-screen-api.transition-duration.leave => 0 0 full-screen-api.transition.timeout => 0 To remove the fullscreen warning: - full-screen-api.warning.timeout => 0 Did you ever notice how long does a video go fullscreen on Firefox? I mean, you double click it, the screen goes black, and a second-ish later the video actually appears.