When the user script loaded, the script can get page informations as a usual javascript. The commonly used page information includes,
* The hostname of the page
var host = window.location.hostname;
* Current url of the page
var url = window.location.href;
* Document url
var url = docuemnt.location.href
* Iterate all the elements
var elms = document.getElementsByTagName('*');
for (var i=0; i<elms.length; i++) {
var elm = elms[i];
//do something
}