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GMT-4 videos won't play in Firefox

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I am trying to watch a video posted on a secure website and I keep getting a message "Firefox on your operating system does not support the video format used in this recording"

I am trying to watch a video posted on a secure website and I keep getting a message "Firefox on your operating system does not support the video format used in this recording"

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Is GMT-4 a format I haven't heard of, or a website I haven't heard of?

It appears you're running Windows XP. Unfortunately, Firefox does not have access to Windows Media Foundation on Windows XP and therefore cannot play H.264/mp4 media.