--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -450,16 +450,19 @@ EventStateManager::ReleaseCurrentIMECont
   }
   mIMEContentObserver = nullptr;
 }
 
 void
 EventStateManager::OnStartToObserveContent(
                      IMEContentObserver* aIMEContentObserver)
 {
+  if (mIMEContentObserver == aIMEContentObserver) {
+    return;
+  }
   ReleaseCurrentIMEContentObserver();
   mIMEContentObserver = aIMEContentObserver;
 }
 
 void
 EventStateManager::OnStopObservingContent(
                      IMEContentObserver* aIMEContentObserver)
 {