--- a/xpcom/threads/nsIThreadManager.idl
+++ b/xpcom/threads/nsIThreadManager.idl
@@ -40,17 +40,17 @@
 
 [ptr] native PRThread(PRThread);
 
 interface nsIThread;
 
 /**
  * An interface for creating and locating nsIThread instances.
  */
-[scriptable, uuid(056216f5-8803-46b4-9199-d95bc1f0446f)]
+[scriptable, uuid(487c10bf-0a22-4148-89fa-790d819dd559)]
 interface nsIThreadManager : nsISupports
 {
   /**
    * Create a new thread (a global, user PRThread).
    *
    * @param creationFlags
    *   Reserved for future use.  Pass 0.
    *
@@ -84,9 +84,15 @@ interface nsIThreadManager : nsISupports
    */
   readonly attribute nsIThread currentThread;
 
   /**
    * This attribute is true if the calling thread is the main thread of the
    * application process.
    */
   readonly attribute boolean isMainThread;
+
+  /**
+   * This attribute is true if the calling thread is the thread on which the
+   * cycle collector runs.
+   */
+  readonly attribute boolean isCycleCollectorThread;
 };

--- a/xpcom/threads/nsThreadManager.cpp
+++ b/xpcom/threads/nsThreadManager.cpp
@@ -300,8 +300,16 @@ nsThreadManager::GetCurrentThread(nsIThr
 NS_IMETHODIMP
 nsThreadManager::GetIsMainThread(PRBool *result)
 {
   // This method may be called post-Shutdown
 
   *result = (PR_GetCurrentThread() == mMainPRThread);
   return NS_OK;
 }
+
+NS_IMETHODIMP
+nsThreadManager::GetIsCycleCollectorThread(PRBool *result)
+{
+  // Not yet implemented.
+  *result = PR_FALSE;
+  return NS_OK;
+}