Comment 68 for bug 224475

For those people whose problem still didn't get fixed after upgrading to flash player 10.2, I have a workaround. You can download an addon called flash game maximizer(for firefox): https://addons.mozilla.org/en-US/firefox/addon/9631/
Then, just edit its settings according to your interests. Press F11 to put firefox in fullscreen and toggle this addon so that its on, and it will be just like a fullscreen flash, but it won't close by changing volume unlike it did with fullscreen flash.