gm_xhr_test.user.js

// ==UserScript==
// @name       CrosDomainUploadTest
// @namespace  http://use.i.E.your.homepage/
// @version    0.1
// @description  enter something useful
// @match      http://dobrochan.com/*
// @copyright  2012+, You
// @grant        GM_xmlhttpRequest
// ==/UserScript==

var stringToByteArray = function(str) {
	"use strict";

	var array = new Uint8Array(str.length),
		i, il;

	for (i = 0, il = str.length; i < il; ++i) {
		array[i] = str.charCodeAt(i) & 0xff;
	}

	return array;
};

var arrayBufferDataUri = function(raw) {
	"use strict";

	var base64 = '',
		encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
		bytes = new Uint8Array(raw),
		byteLength = bytes.byteLength,
		byteRemainder = byteLength % 3,
		mainLength = byteLength - byteRemainder,
		a, b, c, d,
		chunk;

	// Main loop deals with bytes in chunks of 3
	for (var i = 0; i < mainLength; i = i + 3) {
		// Combine the three bytes into a single integer
		chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];

		// Use bitmasks to extract 6-bit segments from the triplet
		a = (chunk & 16515072) >> 18; // 16515072 = (2^6 - 1) << 18
		b = (chunk & 258048) >> 12; // 258048   = (2^6 - 1) << 12
		c = (chunk & 4032) >> 6; // 4032     = (2^6 - 1) << 6
		d = chunk & 63; // 63       = 2^6 - 1
		// Convert the raw binary segments to the appropriate ASCII encoding
		base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d];
	}

	// Deal with the remaining bytes and padding
	if (byteRemainder == 1) {
		chunk = bytes[mainLength];

		a = (chunk & 252) >> 2; // 252 = (2^6 - 1) << 2
		// Set the 4 least significant bits to zero
		b = (chunk & 3) << 4; // 3   = 2^2 - 1
		base64 += encodings[a] + encodings[b] + '==';
	} else if (byteRemainder == 2) {
		chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];

		a = (chunk & 64512) >> 10; // 64512 = (2^6 - 1) << 10
		b = (chunk & 1008) >> 4; // 1008  = (2^6 - 1) << 4
		// Set the 2 least significant bits to zero
		c = (chunk & 15) << 2; // 15    = 2^4 - 1
		base64 += encodings[a] + encodings[b] + encodings[c] + '=';
	}

	return base64;
};

var getURLasAB = function(url, cb) {
	"use strict";

	if (navigator.userAgent.match(/Chrome\/([\d.]+)/)) {
		GM_xmlhttpRequest({
			method: "GET",
			url: url,
			responseType: "arraybuffer",
			onload: function(oEvent) {
				console.log(oEvent);
				cb(oEvent.response);
			},
			onerror: function(oEvent) {
				console.log('url get error');
			}
		});
	} else {
		GM_xmlhttpRequest({
			method: "GET",
			url: url,
			overrideMimeType: "text/plain; charset=x-user-defined",
			onload: function(oEvent) {
				var ff_buffer = stringToByteArray(oEvent.responseText || oEvent.response);
				cb(ff_buffer.buffer);
			},
			onerror: function(oEvent) {
				console.log('url get error');
			}
		});
	}
};

var btn = document.createElement("input");

btn.type = 'button';
btn.value = 'Get URL';
btn.name = 'GetURL';

btn.onclick = function() {
	var url = prompt("URL");
	getURLasAB(url, function(AB) {
		var src = 'data:application/octet-stream;base64,' + arrayBufferDataUri(AB),
			img = document.createElement("img");
		img.src = src;
		document.body.appendChild(img);
	});
};

document.body.appendChild(btn);