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How to disable the full-screen warning message in Firefox

How to disable the full-screen warning message in Firefox

Whenever you watch a full-screen video in Firefox, a warning message appears for a few seconds and then switches off the screen. Although its main purpose is security, you may want to disable the pop-up window if you find it annoying.

What is the full screen warning and why is it important?

All modern browsers use Full screen API to present the desired content, such as videos, images, and online games, using the full screen, without other UI elements. When enabled, a small warning message currently appears at the top of the page, informing you that it has been enabled. This is the same functionality when watching a YouTube video in full screen mode.

Activate full screen mode by clicking the full screen icon.

Although it can sometimes be annoying before continuing and disabling the message in its entirety, it is important to consider its purpose and how it helps prevent phishing attacks.

The only real restriction for developers using the API is that in order to activate full screen mode, the user has to launch it with a click or by pressing a key (keyboard shortcut). The reason for this condition is to prevent incomplete sites from automatically uploading a full screen phishing scam when they access a site.

Unfortunately, this feature is susceptible to a very ingenious phishing attack. Attackers can use the API to show you a fake version of a website in full screen mode, which looks surprisingly like a real deal. All you have to do is click on a legitimate-looking link, and the API loads full screen mode with what looks like a working web browser.

In this case, when the fake site enters full screen mode, the browser displays a warning message notifying you that it has been activated. If you miss the warning, you may think it’s a legitimate site.

If you want to learn more about how the full-screen HTML5 API can be used in phishing attacks, Feross, a programmer who first discovered this, goes into great detail and even has a handy site example. false in Bank of America. on your website.

So now that we’ve figured it all out, if you still want to turn off the warning or simply reduce the time it takes for it to go away, let’s move on.

How to disable the full screen warning message

To continue and disable the full-screen warning message, you’ll need to go to the Advanced Preferences page, which is similar to enabling alerts in Chrome.

Warning: Firefox stores all the settings on this page, so you should be careful when playing here. Changing these settings may be detrimental to the stability and security of your browser. You should only continue if you feel confident and confident in what you are doing.

Scribe about: config in the address bar and then press the Enter key. The page loads with a warning about the impact of changing these preferences and the effect it can have on Firefox. Click the «Accept the risk and continue» button.

Proceed with caution and click "Accept the risks and continue."

In the search bar, type full-screen-api.warning.timeout in the search bar and click the pencil icon next to the result to change the preference value.

Enter full-screen-api.warning.timeout in the search bar and click the pencil icon.

The number you enter is the time in milliseconds until the warning starts to disappear. Note that anything below 500 appears only after the full screen is turned on. For security reasons, if you want to be able to see the warning when you enter full screen mode, you need to put something around 500 milliseconds. Otherwise, enter 0. Click the check mark when you are finished.

Enter an expiration value --- in milliseconds --- and click tick.

After changing the value in the settings, there is no need to restart Firefox. The next time you click a video in full screen mode, the new timeout will be used.

To return to the default expiration, return to the «Advanced Preferences» page and click the reset arrow in the far right of the full screen setup-api.warning.timeout.

Return to the Advanced Preferences page and click the reset arrow in the far right of the full settings-api.warning.timeout screen.


As mentioned above, there are security risks to completely disabling the warning message, as some known phishing scams can take advantage of this vulnerability. Although this threat still exists, it’s probably wise to maintain a timeout that lets you know when something triggers full screen mode in your browser.

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