diff --git a/browser/modules/BrowserUITelemetry.jsm b/browser/modules/BrowserUITelemetry.jsm
index 5bfae91f630..17f07dd8ccb 100644
--- a/browser/modules/BrowserUITelemetry.jsm
+++ b/browser/modules/BrowserUITelemetry.jsm
@@ -130,12 +130,18 @@ this.BrowserUITelemetry = {
   init: function() {
     UITelemetry.addSimpleMeasureFunction("toolbars",
                                          this.getToolbarMeasures.bind(this));
+    Services.obs.addObserver(this, "sessionstore-windows-restored", false);
     Services.obs.addObserver(this, "browser-delayed-startup-finished", false);
   },
 
   observe: function(aSubject, aTopic, aData) {
-    if (aTopic == "browser-delayed-startup-finished") {
-      this._registerWindow(aSubject);
+    switch(aTopic) {
+      case "sessionstore-windows-restored":
+        this._gatherFirstWindowMeasurements();
+        break;
+      case "browser-delayed-startup-finished":
+        this._registerWindow(aSubject);
+        break;
     }
   },
 
@@ -200,16 +206,23 @@ this.BrowserUITelemetry = {
   },
 
   _firstWindowMeasurements: null,
-  _registerWindow: function(aWindow) {
-    // We'll gather measurements on the first non-popup window that opens
-    // after it has painted. We do this here instead of waiting for
-    // UITelemetry to ask for our measurements because at that point
-    // all browser windows have probably been closed, since the vast
-    // majority of saved-session pings are gathered during shutdown.
-    if (!this._firstWindowMeasurements && aWindow.toolbar.visible) {
-      this._firstWindowMeasurements = this._getWindowMeasurements(aWindow);
-    }
+  _gatherFirstWindowMeasurements: function() {
+    // We'll gather measurements as soon as the session has restored.
+    // We do this here instead of waiting for UITelemetry to ask for
+    // our measurements because at that point all browser windows have
+    // probably been closed, since the vast majority of saved-session
+    // pings are gathered during shutdown.
+    let win = RecentWindow.getMostRecentBrowserWindow({
+      private: false,
+      allowPopups: false,
+    });
 
+    // If there are no such windows, we're out of luck. :(
+    this._firstWindowMeasurements = win ? this._getWindowMeasurements(win)
+                                        : {};
+  },
+
+  _registerWindow: function(aWindow) {
     aWindow.addEventListener("unload", this);
     let document = aWindow.document;
 
@@ -419,4 +432,4 @@ function getIDBasedOnFirstIDedAncestor(aNode) {
   }
 
   return aNode.id;
-}
\ No newline at end of file
+}