diff --git a/xpcom/threads/nsIThread.idl b/xpcom/threads/nsIThread.idl
index d4370d489b8..7b91c221175 100644
--- a/xpcom/threads/nsIThread.idl
+++ b/xpcom/threads/nsIThread.idl
@@ -53,18 +53,44 @@ interface nsIRunnable;
 [scriptable, uuid(6be5e380-6886-11d3-9382-00104ba0fd40)]
 interface nsIThread : nsISupports
 {
-    void Join();
-    void Interrupt();
-    attribute PRThreadPriority Priority;
-    readonly attribute PRThreadScope Scope;
-    readonly attribute PRThreadState State;
+    // These must all match the values used in prthread.h
+    const PRUint32 PRIORITY_LOW    = 0;
+    const PRUint32 PRIORITY_NORMAL = 1;
+    const PRUint32 PRIORITY_HIGH   = 2;
+    const PRUint32 PRIORITY_URGENT = 3;
+
+    const PRUint32 SCOPE_LOCAL  = 0;
+    const PRUint32 SCOPE_GLOBAL = 1;
+    const PRUint32 SCOPE_BOUND  = 2;
+
+    const PRUint32 STATE_JOINABLE   = 0;
+    const PRUint32 STATE_UNJOINABLE = 1;
+
+    void join();
+    void interrupt();
+
+    attribute PRThreadPriority       priority;
+    readonly attribute PRThreadScope scope;
+    readonly attribute PRThreadState state;
+    
     [noscript] PRThread GetPRThread();
-    void Init(in nsIRunnable aRunnable,
-              in unsigned long aStackSize,
+    
+    void init(in nsIRunnable aRunnable,
+              in PRUint32 aStackSize,
               in PRThreadPriority aPriority,
               in PRThreadScope    aScope,
               in PRThreadState    aState);
 
+    /*
+     * Get the currently running thread (really a static method sort of thing).
+     */
+    readonly attribute nsIThread currentThread;
+    
+    /*
+     * Sleep to at least this many milliseconds (only works on currrent thread).
+     */
+    void sleep(in PRUint32 msec);
+
 %{C++
     // returns the nsIThread for the current thread:
     static NS_COM nsresult GetCurrent(nsIThread* *result);
diff --git a/xpcom/threads/nsThread.cpp b/xpcom/threads/nsThread.cpp
index 7dd0c7ea1f0..652069afaca 100644
--- a/xpcom/threads/nsThread.cpp
+++ b/xpcom/threads/nsThread.cpp
@@ -49,7 +49,7 @@ PRLogModuleInfo* nsIThreadLog = nsnull;
 ////////////////////////////////////////////////////////////////////////////////
 
 nsThread::nsThread()
-    : mThread(nsnull), mDead(PR_FALSE)
+    : mThread(nsnull), mDead(PR_FALSE), mStartLock(nsnull)
 {
     NS_INIT_REFCNT();
 
@@ -62,10 +62,24 @@ nsThread::nsThread()
         nsIThreadLog = PR_NewLogModule("nsIThread");
     }
 #endif /* PR_LOGGING */
+
+// enforce matching of constants to enums in prthread.h
+NS_ASSERTION(nsIThread::PRIORITY_LOW    == PR_PRIORITY_LOW &&
+             nsIThread::PRIORITY_NORMAL == PRIORITY_NORMAL &&
+             nsIThread::PRIORITY_HIGH   == PRIORITY_HIGH &&
+             nsIThread::PRIORITY_URGENT == PRIORITY_URGENT &&
+             nsIThread::SCOPE_LOCAL  == PR_LOCAL_THREAD &&
+             nsIThread::SCOPE_GLOBAL == PR_GLOBAL_THREAD &&
+             nsIThread::STATE_JOINABLE   == PR_JOINABLE_THREAD &&
+             nsIThread::STATE_UNJOINABLE == PR_UNJOINABLE_THREAD,
+             "Bad constant in nsIThread!");
 }
 
 nsThread::~nsThread()
 {
+    if (mStartLock)
+        PR_DestroyLock(mStartLock);
+
     PR_LOG(nsIThreadLog, PR_LOG_DEBUG,
            ("nsIThread %p destroyed\n", this));
 }
@@ -75,6 +89,8 @@ nsThread::Main(void* arg)
 {
     nsThread* self = (nsThread*)arg;
 
+    self->WaitUntilReadyToStartMain();
+
     nsresult rv = NS_OK;
     rv = self->RegisterThreadSelf();
     NS_ASSERTION(rv == NS_OK, "failed to set thread self");
@@ -212,8 +228,13 @@ nsThread::Init(nsIRunnable* runnable,
     NS_ADDREF_THIS();   // released in nsThread::Exit
     if (state == PR_JOINABLE_THREAD)
         NS_ADDREF_THIS();   // released in nsThread::Join
+    mStartLock = PR_NewLock();
+    if (mStartLock == nsnull)
+        return NS_ERROR_OUT_OF_MEMORY;
+    PR_Lock(mStartLock);
     mThread = PR_CreateThread(PR_USER_THREAD, Main, this,
                               priority, scope, state, stackSize);
+    PR_Unlock(mStartLock);
     PR_LOG(nsIThreadLog, PR_LOG_DEBUG,
            ("nsIThread %p created\n", this));
     if (mThread == nsnull)
@@ -221,6 +242,26 @@ nsThread::Init(nsIRunnable* runnable,
     return NS_OK;
 }
 
+/* readonly attribute nsIThread currentThread; */
+NS_IMETHODIMP 
+nsThread::GetCurrentThread(nsIThread * *aCurrentThread)
+{
+    return GetIThread(PR_CurrentThread(), aCurrentThread);
+}
+
+/* void sleep (in PRUint32 msec); */
+NS_IMETHODIMP 
+nsThread::Sleep(PRUint32 msec)
+{
+    if (PR_CurrentThread() != mThread)
+        return NS_ERROR_FAILURE;
+    
+    if (PR_Sleep(PR_MillisecondsToInterval(msec)) != PR_SUCCESS)
+        return NS_ERROR_FAILURE;
+
+    return NS_OK;
+}
+
 NS_COM nsresult
 NS_NewThread(nsIThread* *result, 
              nsIRunnable* runnable,
@@ -279,6 +320,15 @@ nsThread::RegisterThreadSelf()
     return NS_OK;
 }
 
+void 
+nsThread::WaitUntilReadyToStartMain()
+{
+    PR_Lock(mStartLock);
+    PR_Unlock(mStartLock);
+    PR_DestroyLock(mStartLock);
+    mStartLock = nsnull;
+}
+
 NS_COM nsresult
 nsIThread::GetCurrent(nsIThread* *result)
 {
diff --git a/xpcom/threads/nsThread.h b/xpcom/threads/nsThread.h
index b07b79e1977..dc40ecca2f2 100644
--- a/xpcom/threads/nsThread.h
+++ b/xpcom/threads/nsThread.h
@@ -56,6 +56,7 @@ public:
 
     nsresult RegisterThreadSelf();
     void SetPRThread(PRThread* thread) { mThread = thread; }
+    void WaitUntilReadyToStartMain();
 
     static void PR_CALLBACK Main(void* arg);
     static void PR_CALLBACK Exit(void* arg);
@@ -70,6 +71,7 @@ protected:
     PRThread*                   mThread;
     nsCOMPtr<nsIRunnable>       mRunnable;
     PRBool                      mDead;
+    PRLock*                     mStartLock;
 };
 
 ////////////////////////////////////////////////////////////////////////////////