Many users including ourselves, are having problems installing adobe flash with firefox, it keeps displaying the security errors from Internet explorer although you're installing it for firefox, correct? well the simple and quickest solution is to use this full installer instead on your windows VPS or dedicated server:
http://download.macromedia.com/pub/flashplayer/latest/help/install_flash_player.exe
http://download.macromedia.com/pub/flashplayer/latest/help/install_flash_player.exe