topic Re: Block websites forcing Firefox into full-screen mode in Discussions

Block websites forcing Firefox into full-screen mode

dftf — Tue, 20 Oct 2026 10:46:37 GMT

Following a recent link that was offered on here to a site which pops-open websites to malicious sites, one of them I notice forces Firefox into full-screen mode, and then has one of those "to prove you are human, copy and paste into the Windows "Run" box, or PowerShell, then press ENTER". Similar to this:

I'm surprised to find under about:preferences#permissionsData there is no setting at-all to stop websites from forcing Firefox into full-screen mode!

Can I suggest in a future Firefox version you consider adding a "Full screen" permission item there, and by-default set it to "Default for all websites: [ Ask me to enter full-screen 🔻 ]", and then let people create exceptions for sites they wish to do this automatically? (With other options of: "Never ask me", where a user could then click the settings icon to the left of the URL to do this, similar to silent requests to enable notifications, and "Always allow", the current behaviour.)

Allowing any site to be able to force Firefox into full-screen by-default seems crazy to me, as while a message "Press ESC to exit full-screen" is briefly shown, less-technically-minded users could easily miss that, not realise ESC or F11 can be used to exit that mode and get stuck!

Re: Block websites forcing Firefox into full-screen mode

grundt — Thu, 22 Oct 2026 16:59:50 GMT

I was under the impression that a website could not display fullscreen without some form of user interaction (though that user interaction could be achieved through some form of deception).

Certainly if that's not the case I agree with @dftf that there should be a way to prevent it.

Re: Block websites forcing Firefox into full-screen mode

dftf — Thu, 22 Oct 2026 17:48:14 GMT

@grundt : I tried doing a web-search to see if there was any demo site with a "click here to force browser into full-screen" test page, but couldn't. Found this one though, if the code there works?
https://ccm.net/apps-sites/web/1935-script-to-automatically-display-webpage-in-fullscreen/

If you're feeling brave, you could visit betterfox[.]org with no ad-blocker or script-blockers enabled, and each click on the page should open a new tab to a random website (I'd suggest not downloading any you're asked to). One of the sites it took me to was a similar to the example screenshot, but the moment the site loads, Firefox immediately entered full-screen without me needing to do anything.

(Remove [ and ] in the URL to make it work)