diff --git a/mozilla/widget/src/gtk2/nsWindow.cpp b/mozilla/widget/src/gtk2/nsWindow.cpp
index 2091b6f7965..cbf0cdc0a14 100644
--- a/mozilla/widget/src/gtk2/nsWindow.cpp
+++ b/mozilla/widget/src/gtk2/nsWindow.cpp
@@ -2564,6 +2564,7 @@ nsWindow::NativeCreate(nsIWidget        *aParent,
         }
         else if (mWindowType == eWindowType_popup) {
             mShell = gtk_window_new(GTK_WINDOW_POPUP);
+            gtk_window_set_wmclass(GTK_WINDOW(mShell), "Popup", "Mozilla");
             if (topLevelParent) {
                 gtk_window_set_transient_for(GTK_WINDOW(mShell),
                                             topLevelParent);
@@ -2579,6 +2580,7 @@ nsWindow::NativeCreate(nsIWidget        *aParent,
         else { // must be eWindowType_toplevel
             mShell = gtk_window_new(GTK_WINDOW_TOPLEVEL);
             SetDefaultIcon();
+            gtk_window_set_wmclass(GTK_WINDOW(mShell), "Toplevel", "Mozilla");
 
             // each toplevel window gets its own window group
             mWindowGroup = gtk_window_group_new();
@@ -2784,6 +2786,56 @@ nsWindow::NativeCreate(nsIWidget        *aParent,
     return NS_OK;
 }
 
+NS_IMETHODIMP
+nsWindow::SetWindowClass(const nsAString& aName,
+                         const nsAString &xulWinType)
+{
+  if (!mShell)
+    return NS_ERROR_FAILURE;
+
+  XClassHint *class_hint = XAllocClassHint();
+  if (!class_hint)
+    return NS_ERROR_OUT_OF_MEMORY;
+  const char *role = NULL;
+  class_hint->res_name = ToNewCString(xulWinType);
+  if (!class_hint->res_name) {
+    XFree(class_hint);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  class_hint->res_class = ToNewCString(aName);
+  if (!class_hint->res_class) {
+    nsMemory::Free(class_hint->res_name);
+    XFree(class_hint);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // Parse res_name into a name and role. Characters other than
+  // [A-Za-z0-9_-] are converted to '_'. Anything after the first
+  // colon is assigned to role; if there's no colon, assign the
+  // whole thing to both role and res_name.
+  for (char *c = class_hint->res_name; *c; c++) {
+    if (':' == *c) {
+      *c = 0;
+      role = c + 1;
+    }
+    else if (!isascii(*c) || (!isalnum(*c) && ('_' != *c) && ('-' != *c)))
+      *c = '_';
+  }
+  class_hint->res_name[0] = toupper(class_hint->res_name[0]);
+  if (!role) role = class_hint->res_name;
+
+  gdk_window_set_role(GTK_WIDGET(mShell)->window, role);
+  // Can't use gtk_window_set_wmclass() for this; it prints
+  // a warning & refuses to make the change.
+  XSetClassHint(GDK_DISPLAY(),
+                GDK_WINDOW_XWINDOW(GTK_WIDGET(mShell)->window),
+                class_hint);
+  nsMemory::Free(class_hint->res_class);
+  nsMemory::Free(class_hint->res_name);
+  XFree(class_hint);
+  return NS_OK;
+}
+
 void
 nsWindow::NativeResize(PRInt32 aWidth, PRInt32 aHeight, PRBool  aRepaint)
 {
diff --git a/mozilla/widget/src/gtk2/nsWindow.h b/mozilla/widget/src/gtk2/nsWindow.h
index 8b853fba616..89b5259f344 100644
--- a/mozilla/widget/src/gtk2/nsWindow.h
+++ b/mozilla/widget/src/gtk2/nsWindow.h
@@ -138,6 +138,8 @@ public:
     NS_IMETHOD         SetBorderStyle(nsBorderStyle aBorderStyle);
     NS_IMETHOD         SetTitle(const nsAString& aTitle);
     NS_IMETHOD         SetIcon(const nsAString& aIconSpec);
+    NS_IMETHOD         SetWindowClass(const nsAString& aName,
+                                      const nsAString& xulWinType);
     NS_IMETHOD         SetMenuBar(nsIMenuBar * aMenuBar);
     NS_IMETHOD         ShowMenuBar(PRBool aShow);
     NS_IMETHOD         WidgetToScreen(const nsRect& aOldRect,
diff --git a/mozilla/xpfe/appshell/src/nsXULWindow.cpp b/mozilla/xpfe/appshell/src/nsXULWindow.cpp
index dc5cd525b27..af68a40e6c6 100644
--- a/mozilla/xpfe/appshell/src/nsXULWindow.cpp
+++ b/mozilla/xpfe/appshell/src/nsXULWindow.cpp
@@ -1332,33 +1332,17 @@ void nsXULWindow::StaggerPosition(PRInt32 &aRequestedX, PRInt32 &aRequestedY,
 
 NS_IMETHODIMP nsXULWindow::LoadWindowClassFromXUL()
 {
-  if (mWindow->GetWindowClass(nsnull)==NS_ERROR_NOT_IMPLEMENTED)
-    return NS_OK;
-
   nsCOMPtr<nsIDOMElement> docShellElement;
   GetWindowDOMElement(getter_AddRefs(docShellElement));
   NS_ENSURE_TRUE(docShellElement, NS_ERROR_FAILURE);
 
-  nsAutoString windowClass;
+  nsAutoString windowType;
 
   docShellElement->GetAttribute(NS_LITERAL_STRING("windowtype"),
-                                windowClass);
+                                windowType);
 
-  if (!windowClass.IsEmpty())
-  {
-    PRBool persistPosition;
-    PRBool persistSize;
-    PRBool persistSizeMode;
-
-    if (NS_SUCCEEDED(
-         mContentTreeOwner->
-           GetPersistence(&persistPosition, &persistSize, &persistSizeMode)
-        ) && !persistPosition && !persistSize && !persistSizeMode)
-      windowClass.AppendLiteral("-jsSpamPopupCrap");
-
-    char *windowClass_cstr = ToNewCString(windowClass);
-    mWindow->SetWindowClass(windowClass_cstr);
-    nsMemory::Free(windowClass_cstr);
+  if (!windowType.IsEmpty()) {
+    mWindow->SetWindowClass(NS_LITERAL_STRING("Mozilla"), windowType);
   }
 
   return NS_OK;