diff --git a/ports/cef/browser.rs b/ports/cef/browser.rs
index 6903c63505d..5c7db34abba 100644
--- a/ports/cef/browser.rs
+++ b/ports/cef/browser.rs
@@ -18,6 +18,7 @@ use glutin_app;
 use libc::c_int;
 use std::cell::{Cell, RefCell, BorrowState};
 use std::ptr;
+use std::rc::Rc;
 use std::sync::atomic::{AtomicIsize, Ordering};
 
 thread_local!(pub static ID_COUNTER: AtomicIsize = AtomicIsize::new(0));
@@ -87,6 +88,8 @@ pub struct ServoCefBrowser {
     pub host: CefBrowserHost,
     /// A reference to the browser client.
     pub client: CefClient,
+    /// the glutin window when using windowed rendering
+    pub window: Option<Rc<glutin_app::window::Window>>,
     /// Whether the on-created callback has fired yet.
     pub callback_executed: Cell<bool>,
     /// the display system window handle: only to be used with host.get_window_handle()
@@ -102,11 +105,15 @@ impl ServoCefBrowser {
         let frame = ServoCefFrame::new().as_cef_interface();
         let host = ServoCefBrowserHost::new(client.clone()).as_cef_interface();
         let mut window_handle: cef_window_handle_t = get_null_window_handle();
+        let mut glutin_window: Option<Rc<glutin_app::window::Window>> = None;
 
         let servo_browser = if window_info.windowless_rendering_enabled == 0 {
-            let glutin_window = glutin_app::create_window(window_info.parent_window as glutin_app::WindowID);
-            let servo_browser = Browser::new(Some(glutin_window.clone()));
-            window_handle = glutin_window.platform_window() as cef_window_handle_t;
+            glutin_window = Some(glutin_app::create_window(window_info.parent_window as glutin_app::WindowID));
+            let servo_browser = Browser::new(glutin_window.clone());
+            window_handle = match glutin_window {
+                Some(ref win) => win.platform_window() as cef_window_handle_t,
+                None => get_null_window_handle()
+            };
             ServoBrowser::OnScreen(servo_browser)
         } else {
             ServoBrowser::Invalid
@@ -120,6 +127,7 @@ impl ServoCefBrowser {
             frame: frame,
             host: host,
             client: client,
+            window: glutin_window,
             callback_executed: Cell::new(false),
             servo_browser: RefCell::new(servo_browser),
             message_queue: RefCell::new(vec!()),
@@ -139,9 +147,9 @@ pub trait ServoCefBrowserExtensions {
 impl ServoCefBrowserExtensions for CefBrowser {
     fn init(&self, window_info: &cef_window_info_t) {
         if window_info.windowless_rendering_enabled != 0 {
-            let window = window::Window::new();
-            let servo_browser = Browser::new(Some(window.clone()));
+            let window = window::Window::new(window_info.width, window_info.height);
             window.set_browser(self.clone());
+            let servo_browser = Browser::new(Some(window.clone()));
             *self.downcast().servo_browser.borrow_mut() = ServoBrowser::OffScreen(servo_browser);
         }
 
diff --git a/ports/cef/window.rs b/ports/cef/window.rs
index a8391c3dc37..328152f8067 100644
--- a/ports/cef/window.rs
+++ b/ports/cef/window.rs
@@ -43,6 +43,7 @@ pub static mut DISPLAY: *mut c_void = 0 as *mut c_void;
 #[derive(Clone)]
 pub struct Window {
     cef_browser: RefCell<Option<CefBrowser>>,
+    size: TypedSize2D<DevicePixel,u32>
 }
 
 #[cfg(target_os="macos")]
@@ -77,11 +78,12 @@ fn load_gl() {
 
 impl Window {
     /// Creates a new window.
-    pub fn new() -> Rc<Window> {
+    pub fn new(width: u32, height: u32) -> Rc<Window> {
         load_gl();
 
         Rc::new(Window {
             cef_browser: RefCell::new(None),
+            size: TypedSize2D(width, height)
         })
     }
 
@@ -166,14 +168,36 @@ impl WindowMethods for Window {
     fn framebuffer_size(&self) -> TypedSize2D<DevicePixel,u32> {
         let browser = self.cef_browser.borrow();
         match *browser {
-            None => TypedSize2D(400, 300),
+            None => self.size,
             Some(ref browser) => {
-                let mut rect = cef_rect_t::zero();
-                browser.get_host()
-                       .get_client()
-                       .get_render_handler()
-                       .get_backing_rect((*browser).clone(), &mut rect);
-                TypedSize2D(rect.width as u32, rect.height as u32)
+                if browser.downcast().callback_executed.get() != true {
+                    self.size
+                } else {
+                    let mut rect = cef_rect_t::zero();
+                    rect.width = self.size.width.get() as i32;
+                    rect.height = self.size.height.get() as i32;
+                    if cfg!(target_os="macos") {
+                        // osx relies on virtual pixel scaling to provide sizes different from actual
+                        // pixel size on screen. other platforms are just 1.0 unless the desktop/toolkit says otherwise
+                        if check_ptr_exist!(browser.get_host().get_client(), get_render_handler) &&
+                           check_ptr_exist!(browser.get_host().get_client().get_render_handler(), get_backing_rect) {
+                            browser.get_host()
+                                   .get_client()
+                                   .get_render_handler()
+                                   .get_backing_rect((*browser).clone(), &mut rect);
+                        }
+                    } else {
+                        if check_ptr_exist!(browser.get_host().get_client(), get_render_handler) &&
+                           check_ptr_exist!(browser.get_host().get_client().get_render_handler(), get_view_rect) {
+                            browser.get_host()
+                                   .get_client()
+                                   .get_render_handler()
+                                   .get_view_rect((*browser).clone(), &mut rect);
+                        }
+                    }
+
+                    TypedSize2D(rect.width as u32, rect.height as u32)
+                }
             }
         }
     }