NOTE: This is the XUL method on <browser> / <tabbrowser>, not the global function in chrome://browser/content/browser.js. Please check which one you're documenting! (This one has no post data parameter, see loadURIWithFlags for a version that does)

loadURI( uri, referrer, charset )

Return type: no return value

Load a URL into the document, with the given referrer and character set.

The first argument should be a string, not a nsIURI object. To get a string from an nsIURI, use nsIURI.spec or nsIURI.asciiSpec