diff --git a/xpcom/threads/IdleTaskRunner.cpp b/xpcom/threads/IdleTaskRunner.cpp
index 0ea4b8d425a6..404410bec867 100644
--- a/xpcom/threads/IdleTaskRunner.cpp
+++ b/xpcom/threads/IdleTaskRunner.cpp
@@ -84,6 +84,7 @@ void IdleTaskRunner::SetBudget(int64_t aBudget) {
 
 void IdleTaskRunner::SetTimer(uint32_t aDelay, nsIEventTarget* aTarget) {
   MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aTarget->IsOnCurrentThread());
   // aTarget is always the main thread event target provided from
   // NS_DispatchToCurrentThreadQueue(). We ignore aTarget here to ensure that
   // CollectorRunner always run specifically the main thread.
diff --git a/xpcom/threads/IdleTaskRunner.h b/xpcom/threads/IdleTaskRunner.h
index 7063d7b1dc26..93a55b3d7f4c 100644
--- a/xpcom/threads/IdleTaskRunner.h
+++ b/xpcom/threads/IdleTaskRunner.h
@@ -14,11 +14,10 @@
 
 namespace mozilla {
 
-// A general purpose repeating callback runner (it can be configured
-// to a one-time runner, too.) If it is running repeatedly,
-// one has to either explicitly Cancel() the runner or have
-// MayContinueProcessing() callback return false to completely remove
-// the runner.
+// A general purpose repeating callback runner (it can be configured to a
+// one-time runner, too.) If it is running repeatedly, one has to either
+// explicitly Cancel() the runner or have MayStopProcessing() callback return
+// true to completely remove the runner.
 class IdleTaskRunner final : public CancelableIdleRunnable {
  public:
   // Return true if some meaningful work was done.