How to Disable Firefox’s Full Screen Warning

Firefox there is a full screen mode. This function works perfectly fine and looks harmless, but there are exceptions. That’s because when you enable full screen mode to watch videos on this web browser, you will get a warning. The warning is generated for a reason, but you can also get rid of it if you want.

How to Disable Firefox’s Full Screen Warning

1. What is Fullscreen Warning or Fullscreen Warning? Why is it important?

All modern web browsers use the Fullscreen API to display desired content such as videos, photos, and online games using the entire screen (another type of user interface element). When enabled, a small warning message appears momentarily at the top of the page, notifying you it has been activated. This is the same function when you watch YouTube videos in full screen mode.

Although it can be quite annoying, before you disable the full screen warning, it is important to find out what its purpose is and how it helps prevent phishing attacks.

The only real restriction for developers to use API is that to enable full screen mode, the user needs to initiate it through a mouse click or a keystroke. The reason this condition exists is to prevent “sketchy” websites from automatically loading a scam into full screen when you visit a website.

Unfortunately, this feature is very sensitive to a phishing attack. An attacker can use the API to show you a fake version of a website in full screen mode, which looks exactly like the real version. All you need to do is click on a link that looks legit and the API loads full screen with the look and feel of a working web browser.

In this case, when the fake website goes into full screen mode, the browser will give a warning message that it has been activated. If you ignore this warning, you might think it’s a legitimate website.

After knowing the purpose and importance of this full screen warning, if you still want to disable the full screen warning, here’s how:

2. Turn off Firefox’s full screen warnings

To disable the full screen warning message the full screen warning you will need to visit the page Advanced Preferencessimilar to enabling flags on Chrome.

Note: Firefox keeps all the settings in this page, so you have to be really careful when tinkering here. Changing these settings may affect the stability and security of the browser. You should only continue if you are confident and sure of what you are doing.

You enter about:config in the address bar and press Enter. The web page loads with a warning about the impact of changing these settings and how it affects Firefox. You click on the button Accept the Risk and Continue.

In the search bar, you type full-screen-api.warning.timeout and click on pencil icon next to the result to change the value of the setting.

The number you enter is the amount of time in milliseconds from when the alert appears until it disappears. Remember that a value below 500 will make the warning barely appear after you enable full screen mode. For security reasons, if you want to be able to see warnings when full screen is on, you should set the value to around 500 milliseconds. If not, enter 0. Click Mark when you’re done.

After changing the value in the settings, you don’t need to restart Firefox. The next time you watch a video in full screen, the new timeout will be applied.

To return to the default timeout, go to Advanced Preferences and click on reset arrow located on the right side of the settings full-screen-api.warning.timeout.

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As mentioned, there are security risks to disabling the fullscreen warning message altogether as some phishing scams can take advantage of this vulnerability. For that, you should probably still keep an alert to notify you when anything triggers fullscreen mode in the browser.