--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -2642,18 +2642,18 @@ GeckoDriver.prototype.getWindowSize = fu
  * Not supported on B2G. The supplied width and height values refer to
  * the window outerWidth and outerHeight values, which include scroll
  * bars, title bars, etc.
  *
  * An error will be returned if the requested window size would result
  * in the window being in the maximized state.
  */
 GeckoDriver.prototype.setWindowSize = function(cmd, resp) {
-  if (this.appName !== "Firefox") {
-    throw new UnsupportedOperationError("Not supported on mobile");
+  if (this.appName != "Firefox") {
+    throw new UnsupportedOperationError();
   }
 
   let width = parseInt(cmd.parameters.width);
   let height = parseInt(cmd.parameters.height);
 
   let win = this.getCurrentWindow();
   if (width >= win.screen.availWidth && height >= win.screen.availHeight) {
     throw new UnsupportedOperationError("Invalid requested size, cannot maximize");
@@ -2665,17 +2665,17 @@ GeckoDriver.prototype.setWindowSize = fu
 /**
  * Maximizes the user agent window as if the user pressed the maximise
  * button.
  *
  * Not Supported on B2G or Fennec.
  */
 GeckoDriver.prototype.maximizeWindow = function(cmd, resp) {
   if (this.appName != "Firefox") {
-    throw new UnsupportedOperationError("Not supported for mobile");
+    throw new UnsupportedOperationError();
   }
 
   let win = this.getCurrentWindow();
   win.moveTo(0,0);
   win.resizeTo(win.screen.availWidth, win.screen.availHeight);
 };
 
 /**