--- a/testing/geckodriver/src/marionette.rs
+++ b/testing/geckodriver/src/marionette.rs
@@ -632,17 +632,17 @@ impl MarionetteSession {
             return Err(WebDriverError::new(status, error.message));
         }
 
         try!(self.update(msg, &resp));
 
         Ok(match msg.command {
             // Everything that doesn't have a response value
             Get(_) | GoBack | GoForward | Refresh | SetTimeouts(_) |
-            SetWindowRect(_) | MaximizeWindow | SwitchToWindow(_) | SwitchToFrame(_) |
+            MaximizeWindow | SwitchToWindow(_) | SwitchToFrame(_) |
             SwitchToParentFrame | AddCookie(_) | DeleteCookies | DeleteCookie(_) |
             DismissAlert | AcceptAlert | SendAlertText(_) | ElementClick(_) |
             ElementTap(_) | ElementClear(_) | ElementSendKeys(_, _) |
             PerformActions(_) | ReleaseActions => {
                 WebDriverResponse::Void
             },
             // Things that simply return the contents of the marionette "value" property
             GetCurrentUrl | GetTitle | GetPageSource | GetWindowHandle | IsDisplayed(_) |
@@ -765,16 +765,47 @@ impl MarionetteSession {
                     try_opt!(resp.result.find("height"),
                              ErrorStatus::UnknownError,
                              "Failed to find height field").as_f64(),
                     ErrorStatus::UnknownError,
                     "Failed to interpret width as float");
 
                 WebDriverResponse::ElementRect(ElementRectResponse::new(x, y, width, height))
             },
+            SetWindowRect(_) => {
+                let x = try_opt!(
+                    try_opt!(resp.result.find("x"),
+                             ErrorStatus::UnknownError,
+                             "Failed to find x field").as_f64(),
+                    ErrorStatus::UnknownError,
+                    "Failed to interpret x as float");
+
+                let y = try_opt!(
+                    try_opt!(resp.result.find("y"),
+                             ErrorStatus::UnknownError,
+                             "Failed to find y field").as_f64(),
+                    ErrorStatus::UnknownError,
+                    "Failed to interpret y as float");
+
+                let width = try_opt!(
+                    try_opt!(resp.result.find("width"),
+                             ErrorStatus::UnknownError,
+                             "Failed to find width field").as_f64(),
+                    ErrorStatus::UnknownError,
+                    "Failed to interpret width as float");
+
+                let height = try_opt!(
+                    try_opt!(resp.result.find("height"),
+                             ErrorStatus::UnknownError,
+                             "Failed to find height field").as_f64(),
+                    ErrorStatus::UnknownError,
+                    "Failed to interpret width as float");
+
+                WebDriverResponse::ElementRect(ElementRectResponse::new(x, y, width, height))
+            },
             GetCookies => {
                 let cookies = try!(self.process_cookies(&resp.result));
                 WebDriverResponse::Cookie(CookieResponse::new(cookies))
             },
             GetNamedCookie(ref name) => {
                 let mut cookies = try!(self.process_cookies(&resp.result));
                 cookies.retain(|x| x.name == *name);
                 WebDriverResponse::Cookie(CookieResponse::new(cookies))