--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -1821,37 +1821,42 @@ var UserAgent = {
       }
       case "http-on-modify-request": {
         let channel = aSubject.QueryInterface(Ci.nsIHttpChannel);
         let channelWindow = this._getWindowForRequest(channel);
         let tab = BrowserApp.getTabForWindow(channelWindow);
         if (tab == null)
           break;
 
-      let apps = HelperApps.getAppsForUri(channel.URI);
-      if (apps.length > 0) {
-        let message = apps.length == 1 ? Strings.browser.formatStringFromName("helperapps.openWithApp", [apps[0].name], 1) :
-                                         Strings.browser.GetStringFromName("helperapps.openWithList");
-        let buttons = [{
-            label: Strings.browser.GetStringFromName("helperapps.open"),
-            callback: function() {
-              aSubject.QueryInterface(Ci.nsIRequest).cancel(Components.results.NS_ERROR_ABORT);
-              HelperApps.openUriInApp(channel.URI);
-            }
-          },
-          {
-            label: Strings.browser.GetStringFromName("helperapps.cancel"),
-            callback: function() { }
-        }];
-        // Persist this over page loads. Pages that expect to open in helper apps often redirect
-        // Youtube redirects twice, so I've forced this to two for now
-        let options = { persistence: 2 };
-        let name = "helperapps-" + (apps.length > 1 ? "list" : apps[0].name);
-        NativeWindow.doorhanger.show(message, name, buttons, self.id, options);
-      }
+        let apps = HelperApps.getAppsForUri(channel.URI);
+        if (apps.length > 0) {
+          let message = apps.length == 1 ? Strings.browser.formatStringFromName("helperapps.openWithApp", [apps[0].name], 1) :
+                                           Strings.browser.GetStringFromName("helperapps.openWithList");
+          let buttons = [{
+              label: Strings.browser.GetStringFromName("helperapps.open"),
+              callback: function() {
+                aSubject.QueryInterface(Ci.nsIRequest).cancel(Components.results.NS_ERROR_ABORT);
+                HelperApps.openUriInApp(channel.URI);
+              }
+            },
+            {
+              label: Strings.browser.GetStringFromName("helperapps.cancel"),
+              callback: function() { }
+          }];
+          // Persist this over page loads. Pages that expect to open in helper apps often redirect
+          // Youtube redirects twice, so I've forced this to two for now
+          let options = { persistence: 2 };
+          let name = "helperapps-" + (apps.length > 1 ? "list" : apps[0].name);
+          NativeWindow.doorhanger.show(message, name, buttons, self.id, options);
+        }
+
+        // Send desktop UA if "Request Desktop Site" is enabled
+        if (tab.desktopMode && (channel.loadFlags & Ci.nsIChannel.LOAD_DOCUMENT_URI))
+          channel.setRequestHeader("User-Agent", this.DESKTOP_UA, false);
+        break;
     }
   }
 };
 
 
 function nsBrowserAccess() {
 }