--- a/widget/windows/IMMHandler.cpp
+++ b/widget/windows/IMMHandler.cpp
@@ -2751,18 +2751,19 @@ IMMHandler::OnKeyDownEvent(nsWindow* aWi
       return false;
   }
 }
 
 // static
 void
 IMMHandler::SetCandidateWindow(nsWindow* aWindow, CANDIDATEFORM* aForm)
 {
-  // Hack for ATOK.  ATOK (Japanese IME) refers native caret position at
-  // deciding candidate window position.
+  // Hack for ATOK 2011 - 2016 (Japanese IME).  They refer native caret
+  // position at deciding candidate window position.  Note that we cannot
+  // check active IME since TIPs are wrapped and hidden by CUAS.
   if (aWindow->PluginHasFocus()) {
     // We cannot retrieve proper character height from plugin.  Therefore,
     // we should assume that the caret height is always 20px since if less than
     // this height, candidate window may overlap with composition string when
     // there is no enough space under composition string to show candidate
     // window.
     static const int32_t kCaretHeight = 20;
     if (sNativeCaretIsCreatedForPlugin) {