--- a/dom/xul/XULDocument.cpp
+++ b/dom/xul/XULDocument.cpp
@@ -3016,16 +3016,22 @@ XULDocument::DoneWalking()
                 xulWin->GetDocShell(getter_AddRefs(xulWinShell));
                 if (SameCOMIdentity(xulWinShell, item)) {
                     // We're the chrome document!  Apply our chrome flags now.
                     xulWin->ApplyChromeFlags();
                 }
             }
         }
 
+        nsContentUtils::DispatchTrustedEvent(this,
+                static_cast<nsIDocument*>(this),
+                NS_LITERAL_STRING("MozBeforeInitialXULLayout"),
+                true,
+                false);
+
         StartLayout();
 
         if (mIsWritingFastLoad && IsChromeURI(mDocumentURI))
             nsXULPrototypeCache::GetInstance()->WritePrototype(mMasterPrototype);
 
         NS_ASSERTION(mDelayFrameLoaderInitialization,
                      "mDelayFrameLoaderInitialization should be true!");
         mDelayFrameLoaderInitialization = false;