Firefox wont stay maximized on my second monitor

Rumrunner 24

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Feb 27, 2014
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I'm trying to play netflix and watch streams in full screen on my second monitor while using my main to browse the internet or play games but every time I click or press a button on my keyboard the window on my second monitor exits full screen.
This (http://lifehacker.com/5419028/keep-flash-videos-in-full-screen-on-dual-monitors) seems like it would be a good fix but the site no longer exists and I don't know where to get the .dll I need.
I'm assuming this is expected behavior but it's annoying and I would like to keep my videos in full screen,since my second monitor is only 19 inches.