diff --git a/xpfe/appshell/src/nsXULWindow.cpp b/xpfe/appshell/src/nsXULWindow.cpp
index 3cd09a9f2f27..311eeb849cbf 100644
--- a/xpfe/appshell/src/nsXULWindow.cpp
+++ b/xpfe/appshell/src/nsXULWindow.cpp
@@ -96,6 +96,8 @@
 
 #include "nsWebShellWindow.h" // get rid of this one, too...
 
+#include "prenv.h"
+
 #define SIZEMODE_NORMAL     NS_LITERAL_STRING("normal")
 #define SIZEMODE_MAXIMIZED  NS_LITERAL_STRING("maximized")
 #define SIZEMODE_MINIMIZED  NS_LITERAL_STRING("minimized")
@@ -1387,7 +1389,13 @@ void nsXULWindow::SyncAttributesToWidget()
 
   // "accelerated" attribute
   PRBool isAccelerated;
-  rv = windowElement->HasAttribute(NS_LITERAL_STRING("accelerated"), &isAccelerated);
+  static const char *acceleratedEnv = PR_GetEnv("MOZ_ACCELERATED");
+  if (acceleratedEnv && *acceleratedEnv) {
+    isAccelerated = *acceleratedEnv != '0';
+    rv = NS_OK;
+  } else
+    rv = windowElement->HasAttribute(NS_LITERAL_STRING("accelerated"), &isAccelerated);
+
   if (NS_SUCCEEDED(rv)) {
     mWindow->SetAcceleratedRendering(isAccelerated);
   }