diff --git a/mozilla/xpfe/appshell/public/nsIAppShellService.h b/mozilla/xpfe/appshell/public/nsIAppShellService.h
index ed3c59e5c20..123775208ba 100644
--- a/mozilla/xpfe/appshell/public/nsIAppShellService.h
+++ b/mozilla/xpfe/appshell/public/nsIAppShellService.h
@@ -25,6 +25,7 @@
 #include "nsISupports.h"
 
 /* Forward declarations... */
+struct PRThread;
 class nsIFactory;
 class nsIURL;
 class nsIWebShellWindow;
@@ -47,6 +48,7 @@ public:
   NS_IMETHOD Initialize(nsICmdLineService * aCmdLineService) = 0;
   NS_IMETHOD Run(void) = 0;
   NS_IMETHOD Shutdown(void) = 0;
+  NS_IMETHOD GetPrimordialThread(PRThread **aThread) = 0;
 
   NS_IMETHOD CreateTopLevelWindow(nsIWebShellWindow * aParent,
                                   nsIURL* aUrl, 
diff --git a/mozilla/xpfe/appshell/src/nsAppShellService.cpp b/mozilla/xpfe/appshell/src/nsAppShellService.cpp
index 922288c4627..cd6a7bd36b0 100644
--- a/mozilla/xpfe/appshell/src/nsAppShellService.cpp
+++ b/mozilla/xpfe/appshell/src/nsAppShellService.cpp
@@ -93,6 +93,9 @@ public:
   NS_IMETHOD Initialize(nsICmdLineService*aCmdLineService);
   NS_IMETHOD Run(void);
   NS_IMETHOD Shutdown(void);
+  NS_IMETHOD GetPrimordialThread(PRThread **aThread)
+                { *aThread = mPrimordialThread; return NS_OK; }
+
   NS_IMETHOD CreateTopLevelWindow(nsIWebShellWindow * aParent,
                                   nsIURL* aUrl, 
                                   PRBool showWindow,
@@ -125,6 +128,7 @@ protected:
   nsIAppShell* mAppShell;
   nsISupportsArray* mWindowList;
   nsICmdLineService* mCmdLineService;
+  PRThread* mPrimordialThread;
 };
 
 
@@ -135,6 +139,7 @@ nsAppShellService::nsAppShellService()
   mAppShell     = nsnull;
   mWindowList   = nsnull;
   mCmdLineService = nsnull;
+  mPrimordialThread = nsnull;
 }
 
 nsAppShellService::~nsAppShellService()
@@ -162,6 +167,10 @@ nsAppShellService::Initialize( nsICmdLineService *aCmdLineService )
 #ifdef MOZ_FULLCIRCLE
   FCInitialize();
 #endif
+  // assume no new threads have been spun up yet, or at least if they have,
+  // they haven't been made the current one
+  mPrimordialThread = PR_CurrentThread();
+
   // Remember cmd line service.
   mCmdLineService = aCmdLineService;
   NS_IF_ADDREF( mCmdLineService );