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Viewing media in fullscreen mode adds black borders around the screen.

  • 4 replies
  • 0 have this problem
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  • Last reply by tsedan

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When I play a video in fullscreen, there is a strange black border that appears around the video which makes the content smaller than it would otherwise be. This border does not display in Safari or Chrome, just in Firefox. It also occurs in every media player I've tested, including YouTube and Netflix.

Annoyingly, I can't get this to show up in a screenshot. It seems like Firefox guesses the aspect ratio or resolution wrong when it puts media in fullscreen, and it has the effect of downsizing the actual interactive part of the display. Meaning, I can't move my mouse into the border area to take a screenshot of it.

I'm on an ARM Macbook running MacOS 13.5, if that matters.

Is this a bug, and/or is there a way to fix this?

When I play a video in fullscreen, there is a strange black border that appears around the video which makes the content smaller than it would otherwise be. This border does not display in Safari or Chrome, just in Firefox. It also occurs in every media player I've tested, including YouTube and Netflix. Annoyingly, I can't get this to show up in a screenshot. It seems like Firefox guesses the aspect ratio or resolution wrong when it puts media in fullscreen, and it has the effect of downsizing the actual interactive part of the display. Meaning, I can't move my mouse into the border area to take a screenshot of it. I'm on an ARM Macbook running MacOS 13.5, if that matters. Is this a bug, and/or is there a way to fix this?

Chosen solution

Go to about:config in the address bar and try changing the value of full-screen-api.macos-native-full-screen to true.

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile.

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All Replies (4)

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Use the Recommended Display Resolution. Update Display Drivers. Rollback Display Drivers. Perform a Clean Boot. Time to Reset Windows 10.

Regards, Jimmy

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First off, I don’t have Windows. I also have not touched the display resolution or drivers beyond what Mac ships out-of-the-box. Uninstalling and reinstalling Firefox does not fix the problem, nor does rebooting my machine.

I appreciate the attempt at advice but this did not help with my issue. I have already tried all of the generic troubleshooting methods.

Modified by tsedan

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Chosen Solution

Go to about:config in the address bar and try changing the value of full-screen-api.macos-native-full-screen to true.

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile.

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That fixed it, thanks!