the following code is to load a image from chrome package, and use the
data url to overcome the security control of new FF version.

var loader = {

loadImage : function (url) {
var data = this.loadBinaryResource(url);
var ret = "data:image/"+url.substr(url.lastIndexOf(".")
+1)+";base64,";
try {
data = btoa(data);
}catch (e){
dump(e);
}
ret += data;
return ret;
},
loadBinaryResource : function (url) {
var req = new XMLHttpRequest();
req.open('GET', url, false);
req.overrideMimeType('text/plain; charset=x-user-defined');
try {
req.send(null);
if (req.status != 200) return '';
return req.responseText;
}catch (e){
dump(e);
}
return '';
},
};

but I got 2 exceptions:

1. when url is "chrome://..../.png" it failed. and throw exception. if
the url is "http://...." it can get the resource.

2. after the binary data loaded, while encoding into base64, another
exception thrown.
[Exception... "String contains an invalid character" code: "5"
nsresult: "0x80530005 (NS_ERROR_DOM_INVALID_CHARACTER_ERR)"
location: .....


is there an perfect example to solve the problem?
thanks.