Install .user.js files dropped into the Add-ons Manager.

Refs #1663

content/addons4-overlay.js

@@ -4,6 +4,7 @@
 (function private_scope() {
 Components.utils.import("resource://gre/modules/AddonManager.jsm");
 Components.utils.import("resource://greasemonkey/addons4.js");
+Components.utils.import('resource://greasemonkey/third-party/droppedUrls.js');
 Components.utils.import('resource://greasemonkey/util.js');
 
 var userScriptViewId = 'addons://list/greasemonkey-user-script';
@@ -24,6 +25,21 @@ createItem = function GM_createItem(aObj, aIsInstall, aIsRemote) {
   return item;
 };
 
+// Patch the default onDrop() to make user script installation work.
+var _gDragDrop_onDrop_Orig = gDragDrop.onDrop;
+gDragDrop.onDrop = function GM_onDrop(aEvent) {
+  var urls = droppedUrls(aEvent);
+
+  for (var i = urls.length - 1, url = null; url = urls[i]; i--) {
+    if (url.match(/\.user\.js$/)) {
+      GM_util.showInstallDialog(
+          url, GM_util.getBrowserWindow().gBrowser, GM_util.getService());
+    }
+  }
+
+  _gDragDrop_onDrop_Orig(aEvent);
+};
+
 // Set up an "observer" on the config, to keep the displayed items up to date
 // with their actual state.
 var observer = {

modules/third-party/droppedUrls.js

@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const EXPORTED_SYMBOLS = ['droppedUrls'];
+
+function droppedUrls(aEvent) {
+  var dataTransfer = aEvent.dataTransfer;
+  var urls = [];
+
+  // Convert every dropped item into a url
+  for (var i = 0; i < dataTransfer.mozItemCount; i++) {
+    var url = dataTransfer.mozGetDataAt('text/uri-list', i);
+    if (url) {
+      urls.push(url);
+      continue;
+    }
+
+    url = dataTransfer.mozGetDataAt('text/x-moz-url', i);
+    if (url) {
+      urls.push(url.split('\n')[0]);
+      continue;
+    }
+
+    var file = dataTransfer.mozGetDataAt('application/x-moz-file', i);
+    if (file) {
+      urls.push(Services.io.newFileURI(file).spec);
+      continue;
+    }
+  }
+
+  return urls;
+}