diff --git a/mozilla/netwerk/base/src/nsFileTransportService.cpp b/mozilla/netwerk/base/src/nsFileTransportService.cpp
index 9eee2112c8d..8177495085a 100644
--- a/mozilla/netwerk/base/src/nsFileTransportService.cpp
+++ b/mozilla/netwerk/base/src/nsFileTransportService.cpp
@@ -207,9 +207,10 @@ nsFileTransportService::ProcessPendingRequests(void)
 nsresult
 nsFileTransportService::Shutdown(void)
 {
-    PR_Lock(mLock);
-    mShuttingDown = 1;
-    PR_Unlock(mLock);
+    if (mShuttingDown)
+        return NS_OK;
+
+    mShuttingDown = PR_TRUE;
 
     PRUint32 count;
     mSuspendedTransportList.Count(&count);
diff --git a/mozilla/xpcom/threads/nsThread.cpp b/mozilla/xpcom/threads/nsThread.cpp
index 50b6c54cf90..a4b3b268389 100644
--- a/mozilla/xpcom/threads/nsThread.cpp
+++ b/mozilla/xpcom/threads/nsThread.cpp
@@ -731,12 +731,17 @@ nsThreadPool::Shutdown()
            ("nsIThreadPool thread %p shutting down\n", th.get()));
     
     nsAutoLock lock(mLock);
+    if (mShuttingDown) {
+        NS_ERROR("Bug 166371 - Was Shutdown() called more than once,"
+                 " or did someone forget to call Init()?");
+        return NS_OK;
+    }
     mShuttingDown = PR_TRUE;
     rv = ProcessPendingRequests();
     NS_ASSERTION(NS_SUCCEEDED(rv), "ProcessPendingRequests failed");
     // keep trying... don't bail with an error here
 
-// fix Add assert that there are no more requests to be handled.
+    // fix Add assert that there are no more requests to be handled.
 
     // then interrupt the threads
     rv = mThreads->EnumerateForwards(nsThreadPool::InterruptThreads, nsnull);
@@ -745,13 +750,13 @@ nsThreadPool::Shutdown()
     if (NS_FAILED(rv)) return rv;
     
     while (PR_TRUE) {
-      rv = mThreads->Count(&count);
-      NS_ASSERTION(NS_SUCCEEDED(rv), "Count failed");
-      if (NS_FAILED(rv)) return rv;
-      if (count == 0 )
-          break;
-      PR_WaitCondVar(mThreadExit, PR_INTERVAL_NO_TIMEOUT);
-   }
+        rv = mThreads->Count(&count);
+        NS_ASSERTION(NS_SUCCEEDED(rv), "Count failed");
+        if (NS_FAILED(rv)) return rv;
+        if (count == 0 )
+            break;
+        PR_WaitCondVar(mThreadExit, PR_INTERVAL_NO_TIMEOUT);
+    }
     
     mThreads = nsnull;
     return rv;