Why does Firefox display a fullscreen warning message?
You may see a message like:
You are now fullscreenWebsite is now full screen.
The Fullscreen API is allowed to be activated when a use initiates it. It can either be using the keyboard or with a mouse click. The API allows the website to offer a different version of the website or the player which fits the full-screen method. This mode can be used by a phishing website to automatically go full screen, and offer an interface that may look similar to the real website. Remember that is this different from the F11 function or full-screen mode of Firefox. Here we are talking about video players or anything similar which goes full screen when users press a shortcut or use the mouse.
Disable Fullscreen warning message in Firefox
We will need to access the Advanced Preferences Page, also popularly called the configuration page. These pages are usually not entertained to be used by everyone, and make the changes carefully. If you change the wrong setting, you will have to reset the browser and may lose all your profiles.
However, if you want to reduce the amount of time it stays, you will have to experiment a bit to it figure out. I will suggest keeping the timing such that you get to at least view for a second. It will help if you unluckily land on a bogus website. Once done, next time you go full screen on a video, you will not see any warning. That said, if you would like to revert, go back to the same setting and click on the reset arrow to revert to the default value.