MXHR stands for multiple XmlHttpRequests and was created some days ago by digg.com front end engineers.
This awesome technology lets front end engineers request more than one resource in a single XmlHttpRequest. As an example you will be able, in the future (the project is in alpha release), to get a javascript file, a css and some images with only one request, meaning that you will consume less bandwidth, will get data faster and it will be ordered the way you want. Cool huh?
See more detais on digg’s blog.