diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 27bd4f10004..2d95efbc294 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -3659,6 +3659,8 @@ impl DocumentMethods for Document {
         // Step 10.
         // TODO: prompt to unload.
 
+        window_from_node(self).set_navigation_start();
+
         // Step 11.
         // TODO: unload.
 
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 487bf48eaba..3c87e5f6b0b 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -184,8 +184,8 @@ pub struct Window {
     history: MutNullableJS<History>,
     custom_element_registry: MutNullableJS<CustomElementRegistry>,
     performance: MutNullableJS<Performance>,
-    navigation_start: u64,
-    navigation_start_precise: f64,
+    navigation_start: Cell<u64>,
+    navigation_start_precise: Cell<f64>,
     screen: MutNullableJS<Screen>,
     session_storage: MutNullableJS<Storage>,
     local_storage: MutNullableJS<Storage>,
@@ -702,8 +702,8 @@ impl WindowMethods for Window {
     // NavigationTiming/Overview.html#sec-window.performance-attribute
     fn Performance(&self) -> Root<Performance> {
         self.performance.or_init(|| {
-            Performance::new(self, self.navigation_start,
-                             self.navigation_start_precise)
+            Performance::new(self, self.navigation_start.get(),
+                             self.navigation_start_precise.get())
         })
     }
 
@@ -1772,6 +1772,13 @@ impl Window {
     pub fn unminified_js_dir(&self) -> Option<String> {
         self.unminified_js_dir.borrow().clone()
     }
+
+    pub fn set_navigation_start(&self) {
+        let current_time = time::get_time();
+        let now = (current_time.sec * 1000 + current_time.nsec as i64 / 1000000) as u64;
+        self.navigation_start.set(now);
+        self.navigation_start_precise.set(time::precise_time_ns() as f64);
+    }
 }
 
 impl Window {
@@ -1799,6 +1806,8 @@ impl Window {
                parent_info: Option<(PipelineId, FrameType)>,
                window_size: Option<WindowSizeData>,
                origin: MutableOrigin,
+               navigation_start: u64,
+               navigation_start_precise: f64,
                webvr_thread: Option<IpcSender<WebVRMsg>>)
                -> Root<Window> {
         let layout_rpc: Box<LayoutRPC + Send> = {
@@ -1810,7 +1819,6 @@ impl Window {
             pipelineid: id,
             script_chan: Arc::new(Mutex::new(control_chan)),
         };
-        let current_time = time::get_time();
         let win = box Window {
             globalscope:
                 GlobalScope::new_inherited(
@@ -1837,8 +1845,8 @@ impl Window {
             window_proxy: Default::default(),
             document: Default::default(),
             performance: Default::default(),
-            navigation_start: (current_time.sec * 1000 + current_time.nsec as i64 / 1000000) as u64,
-            navigation_start_precise: time::precise_time_ns() as f64,
+            navigation_start: Cell::new(navigation_start),
+            navigation_start_precise: Cell::new(navigation_start_precise),
             screen: Default::default(),
             session_storage: Default::default(),
             local_storage: Default::default(),
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 722bd2cda12..c5885e64ed0 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -113,7 +113,7 @@ use task_source::file_reading::FileReadingTaskSource;
 use task_source::history_traversal::HistoryTraversalTaskSource;
 use task_source::networking::NetworkingTaskSource;
 use task_source::user_interaction::{UserInteractionTask, UserInteractionTaskSource};
-use time::Tm;
+use time::{get_time, precise_time_ns, Tm};
 use url::Position;
 use webdriver_handlers;
 use webvr_traits::{WebVREvent, WebVRMsg};
@@ -158,6 +158,10 @@ struct InProgressLoad {
     url: ServoUrl,
     /// The origin for the document
     origin: MutableOrigin,
+    /// Timestamp reporting the time when the browser started this load.
+    navigation_start: u64,
+    /// High res timestamp reporting the time when the browser started this load.
+    navigation_start_precise: f64,
 }
 
 impl InProgressLoad {
@@ -170,6 +174,7 @@ impl InProgressLoad {
            window_size: Option<WindowSizeData>,
            url: ServoUrl,
            origin: MutableOrigin) -> InProgressLoad {
+        let current_time = get_time();
         InProgressLoad {
             pipeline_id: id,
             browsing_context_id: browsing_context_id,
@@ -181,6 +186,8 @@ impl InProgressLoad {
             is_visible: true,
             url: url,
             origin: origin,
+            navigation_start: (current_time.sec * 1000 + current_time.nsec as i64 / 1000000) as u64,
+            navigation_start_precise: precise_time_ns() as f64,
         }
     }
 }
@@ -1809,8 +1816,7 @@ impl ScriptThread {
     fn handle_iframe_load_event(&self,
                                 parent_id: PipelineId,
                                 browsing_context_id: BrowsingContextId,
-                                child_id: PipelineId)
-    {
+                                child_id: PipelineId) {
         let iframe = self.documents.borrow().find_iframe(parent_id, browsing_context_id);
         match iframe {
             Some(iframe) => iframe.iframe_load_event_steps(child_id),
@@ -1958,6 +1964,8 @@ impl ScriptThread {
                                  incomplete.parent_info,
                                  incomplete.window_size,
                                  origin,
+                                 incomplete.navigation_start,
+                                 incomplete.navigation_start_precise,
                                  self.webvr_thread.clone());
 
         // Initialize the browsing context for the window.