--- a/browser/base/content/test/performance/browser_startup_flicker.js
+++ b/browser/base/content/test/performance/browser_startup_flicker.js
@@ -10,16 +10,17 @@
 
 add_task(async function() {
   let startupRecorder = Cc["@mozilla.org/test/startuprecorder;1"].getService().wrappedJSObject;
   await startupRecorder.done;
 
   // Ensure all the frame data is in the test compartment to avoid traversing
   // a cross compartment wrapper for each pixel.
   let frames = Cu.cloneInto(startupRecorder.data.frames, {});
+  ok(frames.length > 0, "Should have captured some frames.");
 
   let unexpectedRects = 0;
   let alreadyFocused = false;
   for (let i = 1; i < frames.length; ++i) {
     let frame = frames[i], previousFrame = frames[i - 1];
     let rects = compareFrames(frame, previousFrame);
 
     // The first screenshot we get in OSX / Windows shows an unfocused browser

--- a/browser/components/tests/startupRecorder.js
+++ b/browser/components/tests/startupRecorder.js
@@ -90,26 +90,43 @@ startupRecorder.prototype = {
         firstPaintNotification,
         "sessionstore-windows-restored",
       ];
       for (let t of topics)
         Services.obs.addObserver(this, t);
       return;
     }
 
+    // We only care about the first paint notification for browser windows, and
+    // not other types (for example, the gfx sanity test window)
+    if (topic == firstPaintNotification) {
+      // In the case we're handling xul-window-visible, we'll have been handed
+      // an nsIXULWindow instead of an nsIDOMWindow.
+      if (subject instanceof Ci.nsIXULWindow) {
+        subject = subject.QueryInterface(Ci.nsIInterfaceRequestor)
+                         .getInterface(Ci.nsIDOMWindow);
+      }
+
+      if (subject.document.documentElement.getAttribute("windowtype") != "navigator:browser") {
+        return;
+      }
+    }
+
     if (topic == "image-drawing" || topic == "image-loading") {
       this.data.images[topic].add(data);
       return;
     }
 
     Services.obs.removeObserver(this, topic);
 
     if (topic == firstPaintNotification &&
         Services.prefs.getBoolPref("browser.startup.record", false)) {
-      win = Services.wm.getMostRecentWindow("navigator:browser");
+      // Because of the check for navigator:browser we made earlier, we know
+      // that if we got here, then the subject must be the first browser window.
+      win = subject;
       canvas = win.document.createElementNS("http://www.w3.org/1999/xhtml",
                                             "canvas");
       canvas.mozOpaque = true;
       afterPaintListener();
       win.addEventListener("MozAfterPaint", afterPaintListener);
     }
 
     if (topic == "sessionstore-windows-restored") {

--- a/xpfe/appshell/nsXULWindow.cpp
+++ b/xpfe/appshell/nsXULWindow.cpp
@@ -886,17 +886,18 @@ NS_IMETHODIMP nsXULWindow::SetVisibility
   nsCOMPtr<nsIWindowMediator> windowMediator(do_GetService(NS_WINDOWMEDIATOR_CONTRACTID));
   if (windowMediator)
      windowMediator->UpdateWindowTimeStamp(static_cast<nsIXULWindow*>(this));
 
   // notify observers so that we can hide the splash screen if possible
   nsCOMPtr<nsIObserverService> obssvc = services::GetObserverService();
   NS_ASSERTION(obssvc, "Couldn't get observer service.");
   if (obssvc) {
-    obssvc->NotifyObservers(nullptr, "xul-window-visible", nullptr);
+    obssvc->NotifyObservers(static_cast<nsIXULWindow*>(this),
+                            "xul-window-visible", nullptr);
   }
 
   mDebuting = false;
   return NS_OK;
 }
 
 NS_IMETHODIMP nsXULWindow::GetEnabled(bool *aEnabled)
 {