Firefox Losing Focus

HELP! lol
If I'm running a game through the internet on Firefox and maximize it to full screen, it only stays that way for about 2.5 minutes before it automatically drops back to normal size. Not really a major issue, but quite an inconvenient pain in the @**. Also, when I'm typing, I notice that my window has "lost focus" but not in the traditional sense. It stays with the window I'm on (again, usually Firefox, or IE depending on whether I'm screwing around on games or actually being productive and doing my university courses), but the top bar goes the same as it would if the window was in the background with something else running in front of it. Not sure if this makes sense, but it's really frustrating lol

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