--- a/dom/events/IMEStateManager.cpp
+++ b/dom/events/IMEStateManager.cpp
@@ -188,16 +188,19 @@ IMEStateManager::Shutdown()
 {
   MOZ_LOG(sISMLog, LogLevel::Info,
     ("Shutdown(), sTextCompositions=0x%p, sTextCompositions->Length()=%zu",
      sTextCompositions, sTextCompositions ? sTextCompositions->Length() : 0));
 
   MOZ_ASSERT(!sTextCompositions || !sTextCompositions->Length());
   delete sTextCompositions;
   sTextCompositions = nullptr;
+  // All string instances in the global space need to be empty after XPCOM
+  // shutdown.
+  sActiveChildInputContext.ShutDown();
 }
 
 // static
 void
 IMEStateManager::OnTabParentDestroying(TabParent* aTabParent)
 {
   if (sFocusedIMETabParent == aTabParent) {
     NotifyIMEOfBlurForChildProcess();

--- a/widget/IMEData.h
+++ b/widget/IMEData.h
@@ -274,16 +274,28 @@ struct InputContext final
 {
   InputContext()
     : mOrigin(XRE_IsParentProcess() ? ORIGIN_MAIN : ORIGIN_CONTENT)
     , mMayBeIMEUnaware(false)
     , mInPrivateBrowsing(false)
   {
   }
 
+  // If InputContext instance is a static variable, any heap allocated stuff
+  // of its members need to be deleted at XPCOM shutdown.  Otherwise, it's
+  // detected as memory leak.
+  void ShutDown()
+  {
+    // The buffer for nsString will be released with a call of SetCapacity(0).
+    // Truncate() isn't enough because it just sets length to 0.
+    mHTMLInputType.SetCapacity(0);
+    mHTMLInputInputmode.SetCapacity(0);
+    mActionHint.SetCapacity(0);
+  }
+
   bool IsPasswordEditor() const
   {
     return mHTMLInputType.LowerCaseEqualsLiteral("password");
   }
 
   IMEState mIMEState;
 
   /* The type of the input if the input is a html input field */