thats known as zooming in, its possible that you accidently clicked the wrong button or something, anyways just right-click on the game and select the "show all" or "zoom out" button, your problem should then be fixed, if not, then it might be a problem related to your adobe flash player, so make sure you have the latest version, which is 10.3.
assuming you dont have the latest flash version, here is the link to the download for the latest version of adobe flash player: http://get.adobe.com/flashplayer/
if you do have the latest adobe flash player then it is possible that an add-on/plugin on your firefox browser is interfering with the adobe flash player plugin, so, if your firefox version is 3.6 to 3.6.19 then go to tools > addons, if it is firefox 4 or 5, then click on the firefox button at the top left of the screen and go to addons once there, disable all of your add-ons and plugins in your firefox browser, and keep the flash player plugin enabled, restart the browser and load up a random game, if it works, then a plugin/addon was interfering with the flash player plugin, so re-enable 1 plugin and addon at a time until you find the addon interfering with your flash player.
if your flash player still doesnt work even after disabling all addons and plugins, then the flash player itself may be corrupted, in which you will have to completely uninstall the flash player and reinstall it with the latest version your problem should then be fixed.
if that still doesnt work then a program running in the background might be interfering with the flash player, so download this program known as the game booster, the download link is here: http://download.cnet.com/Game-Booster/3 ... 13645.html
once it is all setup, disable all processes and load up a game again, if it works than a program running in the background is interfering with adobe flash player, so as before with the addons and plugins, enable each process one by one until you find the one interfering with adobe flash player, after that your problem should be fix.
if that doesnt work, try reinstalling all programs required to run web applications, which is all browser except internet explorer, java, adobe programs, and so on, after you reinstall them and setup your browsers up again, load up a random game and it should work.
if that doesnt work, then you will need to do a system restore, havent used windows xp in a long time so i forgot where it is in windows xp, but for windows vista go to start menu > control panel > system and maintenance > backup and restore, then look on the side panel to the left and select 'repair windows using system restore', as for windows xp, go to start menu and type in the search bar 'system restore' should be able to find it from there, once you are there, select a 'check point' and confirm, after all of that, load up a random game and it should work.
if all of this doesnt work, search the web using ask, google, or bing to find an answer to your problem.