So... this appears to do little more than normalize prefixes. So why not just throw a normalization gist up? The first part is: HTMLElement.prototype.requestFullscreen = HTMLElement.prototype.requestFullscreen || HTMLElement.prototype.webkitRequestFullscreen || HTMLElement.prototype.webkitRequestFullScreen || HTMLElement.prototype.mozRequestFullScreen;
It does way more normalizing than just the name of the function. It works around a number of bugs when the element is in an iframe, and it has a fallback if you're using it for video (which was the main reason I wrote it).
I also like the idea of an option to fall back to making the element fill the page if the browser doesn't support the fullscreen API. You could even breifly display the hotkey to put the browser window in fullscreen if it supports it.