From: timeless@mozdev.org

Bug 480851 ASSERTION: "You can't dereference a NULL nsCOMPtr with operator->()" with Firebug installed [@ DEBUG_CheckWrapperThreadSafety]

diff --git a/js/src/xpconnect/src/nsXPConnect.cpp b/js/src/xpconnect/src/nsXPConnect.cpp
--- a/js/src/xpconnect/src/nsXPConnect.cpp
+++ b/js/src/xpconnect/src/nsXPConnect.cpp
@@ -51,18 +51,21 @@
 #include "jsfun.h"
 #include "jsscript.h"
 #include "nsThreadUtilsInternal.h"
+#include "nsIObserverService.h"
 #include "dom_quickstubs.h"
 
-NS_IMPL_THREADSAFE_ISUPPORTS6(nsXPConnect,
+NS_IMPL_THREADSAFE_ISUPPORTS7(nsXPConnect,
                               nsIXPConnect,
                               nsISupportsWeakReference,
                               nsIThreadObserver,
                               nsIJSRuntimeService,
                               nsIJSContextStack,
-                              nsIThreadJSContextStack)
+                              nsIThreadJSContextStack,
+                              nsIObserver)
 
 nsXPConnect* nsXPConnect::gSelf = nsnull;
 JSBool       nsXPConnect::gOnceAliveNowDead = JS_FALSE;
+JSBool       nsXPConnect::gThreadsGone = JS_FALSE;
 PRUint32     nsXPConnect::gReportAllJSExceptions = 0;
 
 // Global cache of the default script security manager (QI'd to
@@ -122,6 +125,13 @@ nsXPConnect::nsXPConnect()
     char* reportableEnv = PR_GetEnv("MOZ_REPORT_ALL_JS_EXCEPTIONS");
     if(reportableEnv && *reportableEnv)
         gReportAllJSExceptions = 1;
+
+    {
+        nsCOMPtr<nsIObserverService> os(do_GetService("@mozilla.org/observer-service;1"));
+        if (os) {
+            os->AddObserver(this, "xpcom-shutdown-threads", PR_TRUE);
+        }
+    }
 }
 
 nsXPConnect::~nsXPConnect()
@@ -2641,6 +2651,22 @@ nsXPConnect::SetSafeJSContext(JSContext 
     return data->GetJSContextStack()->SetSafeJSContext(aSafeJSContext);
 }
 
+/* void observe(); */
+NS_IMETHODIMP
+nsXPConnect::Observe(nsISupports* aSubject, const char* aTopic, const PRUnichar* aData)
+{
+    if (!aTopic)
+        return NS_OK;
+
+    nsDependentCString topic(aTopic);
+    if (topic.EqualsLiteral("xpcom-shutdown-threads")) {
+        gThreadsGone = JS_TRUE;
+        return NS_OK;
+    }
+
+    return NS_OK;
+}
+
 nsIPrincipal*
 nsXPConnect::GetPrincipal(JSObject* obj, PRBool allowShortCircuit) const
 {
diff --git a/js/src/xpconnect/src/xpcprivate.h b/js/src/xpconnect/src/xpcprivate.h
--- a/js/src/xpconnect/src/xpcprivate.h
+++ b/js/src/xpconnect/src/xpcprivate.h
@@ -104,6 +104,7 @@
 #include "nsIConsoleService.h"
 #include "nsIScriptError.h"
 #include "nsIExceptionService.h"
+#include "nsIObserver.h"
 
 #include "nsVariant.h"
 #include "nsIPropertyBag.h"
@@ -457,7 +458,8 @@ class nsXPConnect : public nsIXPConnect,
                     public nsCycleCollectionJSRuntime,
                     public nsCycleCollectionParticipant,
                     public nsIJSRuntimeService,
-                    public nsIThreadJSContextStack
+                    public nsIThreadJSContextStack,
+                    public nsIObserver
 {
 public:
     // all the interface method declarations...
@@ -467,6 +469,7 @@ public:
     NS_DECL_NSIJSRUNTIMESERVICE
     NS_DECL_NSIJSCONTEXTSTACK
     NS_DECL_NSITHREADJSCONTEXTSTACK
+    NS_DECL_NSIOBSERVER
 
     // non-interface implementation
 public:
@@ -564,6 +567,7 @@ private:
     // Singleton instance
     static nsXPConnect*      gSelf;
     static JSBool            gOnceAliveNowDead;
+    static JSBool            gThreadsGone;
 
     XPCJSRuntime*            mRuntime;
     nsCOMPtr<nsIInterfaceInfoSuperManager> mInterfaceInfoManager;
diff --git a/js/src/xpconnect/src/xpcwrappednative.cpp b/js/src/xpconnect/src/xpcwrappednative.cpp
--- a/js/src/xpconnect/src/xpcwrappednative.cpp
+++ b/js/src/xpconnect/src/xpcwrappednative.cpp
@@ -3687,6 +3687,9 @@ void DEBUG_ReportWrapperThreadSafetyErro
 
 void DEBUG_CheckWrapperThreadSafety(const XPCWrappedNative* wrapper)
 {
+    if(nsXPConnect::gThreadsGone)
+        return;
+
     XPCWrappedNativeProto* proto = wrapper->GetProto();
     if(proto && proto->ClassIsThreadSafe())
         return;