GSAP itself is pure JavaScript and should work in virtually ALL browsers. GSAP wasn’t intended to solve all browser incompatibilities, but it does implement wizardry for critical features like opacity, transforms (rotation, scaleX, scaleY, skewX, skewY, x, and y), and transformOrigin so those should work in all major browsers even back to IE6. Firefox doesn’t support backgroundPositionX or backgroundPositionY, so those specific properties won’t work but backgroundPosition will for virtually all browsers. There is NOT a predetermined list of css properties that you can tween – the platform will attempt to tween ANY property you pass in. If it is numeric, it will tween it. If it isn’t numeric and it isn’t a recognized special property, CSSPlugin will just set the property to the value you provide (without tweening it). So, for example, if you try to tween to display:"inline", that isn’t a tweenable property but it will still be set accordingly during the tween, so feel free to use that to your advantage.

LoaderMax is included in the main AS3 GreenSock download zip.

The first parameter of the various loaders (ImageLoader, XMLLoader, SWFLoader, MP3Loader, etc.) accepts either a simple String URL or a URLRequest. So if you want to pass data to the server, simply construct a URLRequest accordingly, like:

var request:URLRequest = new URLRequest("http://www.yourDomain.com/whatever.php");
var data:URLVariables = new URLVariables();
data.exampleSessionId = new Date().getTime();
data.exampleUserLabel = "label1";
request.data = data;
request.method = URLRequestMethod.POST;
var loader:ImageLoader = new ImageLoader(request, {name:"image1"});

Yes.