document.load()
is a part of an old version of the W3C DOM Level 3 Load & Save module. Can be used with document.async to indicate whether the request is synchronous or asynchronous (the default). As of at least Gecko 1.9, this no longer supports cross-site loading of documents (Use XMLHttpRequest instead).
Examples
See also the load sample in the XML tests directory. (To test this functionality, create the files on your local disk or on a webserver rather than loading the load.html file from the LXR-generated page, which will serve the text.xml file as HTML.)