diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index f8bf14a4f..1032c4b33 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -11537,10 +11537,20 @@ nsGlobalWindow::SetInterval(JSContext* aCx, const nsAString& aHandler,
   return SetTimeoutOrInterval(aCx, aHandler, timeout, isInterval, aError);
 }
 
+// TenFourFox issue 463
 nsresult
 nsGlobalWindow::SetTimeoutOrInterval(nsIScriptTimeoutHandler *aHandler,
                                      int32_t interval,
                                      bool aIsInterval, int32_t *aReturn)
+{
+  return SetTimeoutOrIntervalOrIdleCallback(aHandler, interval, aIsInterval, aReturn, nullptr);
+}
+
+nsresult
+nsGlobalWindow::SetTimeoutOrIntervalOrIdleCallback(nsIScriptTimeoutHandler *aHandler,
+                                                   int32_t interval,
+                                                   bool aIsInterval, int32_t *aReturn,
+                                                   mozilla::dom::IdleRequestCallback *aCallback)
 {
   MOZ_ASSERT(IsInnerWindow());
 
@@ -11565,7 +11575,10 @@ nsGlobalWindow::SetTimeoutOrInterval(nsIScriptTimeoutHandler *aHandler,
   RefPtr<nsTimeout> timeout = new nsTimeout();
   timeout->mIsInterval = aIsInterval;
   timeout->mInterval = interval;
-  timeout->mScriptHandler = aHandler;
+  if (aCallback)
+    timeout->mCallback = aCallback;
+  else
+    timeout->mScriptHandler = aHandler;
 
   // Now clamp the actual interval we will use for the timer based on
   uint32_t nestingLevel = sNestingLevel + 1;
@@ -11754,6 +11767,13 @@ nsGlobalWindow::RunTimeoutHandler(nsTimeout* aTimeout,
     reason = "setTimeout handler";
   }
 
+  if (!timeout->mScriptHandler) {
+    // Time to assess the conditions for requestIdleCallback (issue 463).
+    MOZ_ASSERT(timeout->mCallback);
+    MOZ_CRASH("RunTimeoutHandler triggered on requestIdleCallback");
+    return false;
+  }
+
   nsCOMPtr<nsIScriptTimeoutHandler> handler(timeout->mScriptHandler);
   RefPtr<Function> callback = handler->GetCallback();
   if (!callback) {
diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index 41d1b65e4..025b261fa 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -211,7 +211,10 @@ public:
   PopupControlState mPopupState;
 
   // The language-specific information about the callback.
+  // If there is an nsIScriptTimeoutHandler, this is a regular setTimeout.
+  // If there is an IdleRequestCallback, this is requestIdleCallback (issue 463).
   nsCOMPtr<nsIScriptTimeoutHandler> mScriptHandler;
+  RefPtr<mozilla::dom::IdleRequestCallback> mCallback;
 };
 
 struct IdleObserverHolder
@@ -1411,6 +1414,12 @@ public:
   nsresult SetTimeoutOrInterval(nsIScriptTimeoutHandler *aHandler,
                                 int32_t interval,
                                 bool aIsInterval, int32_t* aReturn) override;
+  // TenFourFox issue 463
+  nsresult SetTimeoutOrIntervalOrIdleCallback(nsIScriptTimeoutHandler *aHandler,
+                                              int32_t interval,
+                                              bool aIsInterval, int32_t *aReturn,
+                                              mozilla::dom::IdleRequestCallback *aCallback);
+
   int32_t SetTimeoutOrInterval(JSContext* aCx,
                                mozilla::dom::Function& aFunction,
                                int32_t aTimeout,