There are a few differences in how you obtain the browser object that allows you to make the async call back to the server, but all intro tutorials seem to have "if/then/else" blocks in their examples to help you get around getting this object. (Of course, old-enough browsers can't do ajax at all.) Depending on what you are doing with the response to the async call you just made, there can be minor variations in the javscript methods you call to manipulate the DOM, but then you say you're aware of that level already. The bottom line is that it really isn't any trickier for cross-browser ajax than it already is for cross-browser js, from what I've seen and done with it.