diff --git a/xpcom/threads/nsEventQueue.cpp b/xpcom/threads/nsEventQueue.cpp
index 6ba238d1e9a7..4c68e5156414 100644
--- a/xpcom/threads/nsEventQueue.cpp
+++ b/xpcom/threads/nsEventQueue.cpp
@@ -80,48 +80,40 @@ nsEventQueue::GetEvent(bool mayWait, nsIRunnable **result)
   return true;
 }
 
-bool
+void
 nsEventQueue::PutEvent(nsIRunnable *runnable)
 {
   // Avoid calling AddRef+Release while holding our monitor.
   nsRefPtr<nsIRunnable> event(runnable);
-  bool rv = true;
-  {
-    if (ChaosMode::isActive()) {
-      // With probability 0.5, yield so other threads have a chance to
-      // dispatch events to this queue first.
-      if (ChaosMode::randomUint32LessThan(2)) {
-        PR_Sleep(PR_INTERVAL_NO_WAIT);
-      }
-    }
 
-    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
-
-    if (!mHead) {
-      mHead = NewPage();
-      if (!mHead) {
-        rv = false;
-      } else {
-        mTail = mHead;
-        mOffsetHead = 0;
-        mOffsetTail = 0;
-      }
-    } else if (mOffsetTail == EVENTS_PER_PAGE) {
-      Page *page = NewPage();
-      if (!page) {
-        rv = false;
-      } else {
-        mTail->mNext = page;
-        mTail = page;
-        mOffsetTail = 0;
-      }
-    }
-    if (rv) {
-      event.swap(mTail->mEvents[mOffsetTail]);
-      ++mOffsetTail;
-      LOG(("EVENTQ(%p): notify\n", this)); 
-      mon.NotifyAll();
+  if (ChaosMode::isActive()) {
+    // With probability 0.5, yield so other threads have a chance to
+    // dispatch events to this queue first.
+    if (ChaosMode::randomUint32LessThan(2)) {
+      PR_Sleep(PR_INTERVAL_NO_WAIT);
     }
   }
-  return rv;
+
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+  if (!mHead) {
+    mHead = NewPage();
+    MOZ_ASSERT(mHead);
+
+    mTail = mHead;
+    mOffsetHead = 0;
+    mOffsetTail = 0;
+  } else if (mOffsetTail == EVENTS_PER_PAGE) {
+    Page *page = NewPage();
+    MOZ_ASSERT(page);
+
+    mTail->mNext = page;
+    mTail = page;
+    mOffsetTail = 0;
+  }
+
+  event.swap(mTail->mEvents[mOffsetTail]);
+  ++mOffsetTail;
+  LOG(("EVENTQ(%p): notify\n", this)); 
+  mon.NotifyAll();
 }
diff --git a/xpcom/threads/nsEventQueue.h b/xpcom/threads/nsEventQueue.h
index f261a1bb83bf..5a9bf5adf4a3 100644
--- a/xpcom/threads/nsEventQueue.h
+++ b/xpcom/threads/nsEventQueue.h
@@ -20,11 +20,10 @@ public:
   nsEventQueue();
   ~nsEventQueue();
 
-  // This method adds a new event to the pending event queue.  The event object
-  // is AddRef'd if this method succeeds.  This method returns true if the
-  // event was stored in the event queue, and it returns false if it could
-  // not allocate sufficient memory.
-  bool PutEvent(nsIRunnable *event);
+  // This method adds a new event to the pending event queue.  The queue holds
+  // a strong reference to the event after this method returns.  This method
+  // cannot fail.
+  void PutEvent(nsIRunnable *event);
 
   // This method gets an event from the event queue.  If mayWait is true, then
   // the method will block the calling thread until an event is available.  If
@@ -44,11 +43,6 @@ public:
     return GetEvent(false, runnable);
   }
 
-  // This method waits for and returns the next pending event.
-  bool WaitPendingEvent(nsIRunnable **runnable) {
-    return GetEvent(true, runnable);
-  }
-
   // Expose the event queue's monitor for "power users"
   ReentrantMonitor& GetReentrantMonitor() {
     return mReentrantMonitor;
@@ -73,7 +67,7 @@ private:
                 "sizeof(Page) should be a power of two to avoid heap slop.");
 
   static Page *NewPage() {
-    return static_cast<Page *>(calloc(1, sizeof(Page)));
+    return static_cast<Page *>(moz_xcalloc(1, sizeof(Page)));
   }
 
   static void FreePage(Page *p) {
diff --git a/xpcom/threads/nsThread.cpp b/xpcom/threads/nsThread.cpp
index b577727a3d83..c01d6fb69cb0 100644
--- a/xpcom/threads/nsThread.cpp
+++ b/xpcom/threads/nsThread.cpp
@@ -432,8 +432,7 @@ nsThread::PutEvent(nsIRunnable *event, nsNestedEventTarget *target)
       NS_WARNING("An event was posted to a thread that will never run it (rejected)");
       return NS_ERROR_UNEXPECTED;
     }
-    if (!queue->PutEvent(event))
-      return NS_ERROR_OUT_OF_MEMORY;
+    queue->PutEvent(event);
   }
 
   nsCOMPtr<nsIThreadObserver> obs = GetObserver();
diff --git a/xpcom/threads/nsThread.h b/xpcom/threads/nsThread.h
index 714fef38ec65..0c3c839a1d50 100644
--- a/xpcom/threads/nsThread.h
+++ b/xpcom/threads/nsThread.h
@@ -97,8 +97,8 @@ protected:
       return mQueue.GetEvent(mayWait, event);
     }
 
-    bool PutEvent(nsIRunnable *event) {
-      return mQueue.PutEvent(event);
+    void PutEvent(nsIRunnable *event) {
+      mQueue.PutEvent(event);
     }
 
     bool HasPendingEvent() {