--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -3393,16 +3393,22 @@ pref("intl.tsf.enable", true);
 
 // Support IMEs implemented with IMM in TSF mode.
 pref("intl.tsf.support_imm", true);
 
 // Enables/Disables hack for specific TIP.
 
 // Whether creates native caret for ATOK or not.
 pref("intl.tsf.hack.atok.create_native_caret", true);
+// Whether use available composition string rect for result of
+// ITfContextView::GetTextExt() even if the specified range is same as the
+// range of composition string but some character rects of them are not
+// available.  Note that this is ignored if active ATOK is or older than 2016
+// and create_native_caret is true.
+pref("intl.tsf.hack.atok.do_not_return_no_layout_error_of_composition_string", true);
 // Whether use composition start position for the result of
 // ITfContextView::GetTextExt() if the specified range is larger than
 // composition start offset.
 // For Free ChangJie 2010
 pref("intl.tsf.hack.free_chang_jie.do_not_return_no_layout_error", true);
 // For Microsoft Pinyin and Microsoft Wubi
 pref("intl.tsf.hack.ms_simplified_chinese.do_not_return_no_layout_error", true);
 // For Microsoft ChangJie and Microsoft Quick

--- a/widget/windows/TSFTextStore.cpp
+++ b/widget/windows/TSFTextStore.cpp
@@ -1259,16 +1259,17 @@ StaticRefPtr<ITfDisplayAttributeMgr> TSF
 StaticRefPtr<ITfCategoryMgr> TSFTextStore::sCategoryMgr;
 StaticRefPtr<ITfDocumentMgr> TSFTextStore::sDisabledDocumentMgr;
 StaticRefPtr<ITfContext> TSFTextStore::sDisabledContext;
 StaticRefPtr<ITfInputProcessorProfiles> TSFTextStore::sInputProcessorProfiles;
 StaticRefPtr<TSFTextStore> TSFTextStore::sEnabledTextStore;
 DWORD TSFTextStore::sClientId  = 0;
 
 bool TSFTextStore::sCreateNativeCaretForLegacyATOK = false;
+bool TSFTextStore::sDoNotReturnNoLayoutErrorToATOKOfCompositionString = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToMSSimplifiedTIP = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToMSTraditionalTIP = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToFreeChangJie = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToEasyChangjei = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtFirstChar = false;
 bool TSFTextStore::sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtCaret = false;
 bool TSFTextStore::sHackQueryInsertForMSSimplifiedTIP = false;
 bool TSFTextStore::sHackQueryInsertForMSTraditionalTIP = false;
@@ -3737,16 +3738,32 @@ TSFTextStore::GetTextExt(TsViewCookie vc
           return E_FAIL;
         }
         int32_t minOffsetOfLayoutChanged =
           static_cast<int32_t>(mContentForTSF.MinOffsetOfLayoutChanged());
         acpEnd = acpStart = std::max(minOffsetOfLayoutChanged - 1, 0);
         dontReturnNoLayoutError = true;
       }
     }
+    // ATOK fails to handle TS_E_NOLAYOUT only when it decides the position of
+    // suggest window.  In such case, ATOK tries to query rect of whole
+    // composition string.
+    // XXX For testing with legacy ATOK, we should hack it even if current ATOK
+    //     refers native caret rect on windows whose window class is one of
+    //     Mozilla window classes and we stop creating native caret for ATOK
+    //     because creating native caret causes ATOK refers caret position
+    //     when GetTextExt() returns TS_E_NOLAYOUT.
+    else if (sDoNotReturnNoLayoutErrorToATOKOfCompositionString &&
+             kSink->IsATOKActive() &&
+             (!kSink->IsATOKReferringNativeCaretActive() ||
+              !sCreateNativeCaretForLegacyATOK) &&
+             mComposition.mStart == acpStart &&
+             mComposition.EndOffset() == acpEnd) {
+      dontReturnNoLayoutError = true;
+    }
     // Free ChangJie 2010 and Easy Changjei 1.0.12.0 doesn't handle
     // ITfContextView::GetTextExt() properly.  Prehaps, it's due to the bug of
     // TSF.  We need to check if this is necessary on Windows 10 before
     // disabling this on Windows 10.
     else if ((sDoNotReturnNoLayoutErrorToFreeChangJie &&
               kSink->IsFreeChangJieActive()) ||
              (sDoNotReturnNoLayoutErrorToEasyChangjei &&
               kSink->IsEasyChangjeiActive())) {
@@ -5746,16 +5763,20 @@ TSFTextStore::Initialize()
   sKeystrokeMgr = keystrokeMgr;
   sDisplayAttrMgr = displayAttributeMgr;
   sCategoryMgr = categoryMgr;
   sDisabledDocumentMgr = disabledDocumentMgr;
   sDisabledContext = disabledContext;
 
   sCreateNativeCaretForLegacyATOK =
     Preferences::GetBool("intl.tsf.hack.atok.create_native_caret", true);
+  sDoNotReturnNoLayoutErrorToATOKOfCompositionString =
+    Preferences::GetBool(
+      "intl.tsf.hack.atok.do_not_return_no_layout_error_of_composition_string",
+      true);
   sDoNotReturnNoLayoutErrorToMSSimplifiedTIP =
     Preferences::GetBool(
       "intl.tsf.hack.ms_simplified_chinese.do_not_return_no_layout_error",
       true);
   sDoNotReturnNoLayoutErrorToMSTraditionalTIP =
     Preferences::GetBool(
       "intl.tsf.hack.ms_traditional_chinese.do_not_return_no_layout_error",
       true);
@@ -5780,23 +5801,25 @@ TSFTextStore::Initialize()
     Preferences::GetBool(
       "intl.tsf.hack.ms_traditional_chinese.query_insert_result", true);
 
   MOZ_LOG(sTextStoreLog, LogLevel::Info,
     ("  TSFTextStore::Initialize(), sThreadMgr=0x%p, "
      "sClientId=0x%08X, sDisplayAttrMgr=0x%p, "
      "sCategoryMgr=0x%p, sDisabledDocumentMgr=0x%p, sDisabledContext=%p, "
      "sCreateNativeCaretForLegacyATOK=%s, "
+     "sDoNotReturnNoLayoutErrorToATOKOfCompositionString=%s, "
      "sDoNotReturnNoLayoutErrorToFreeChangJie=%s, "
      "sDoNotReturnNoLayoutErrorToEasyChangjei=%s, "
      "sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtFirstChar=%s, "
      "sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtCaret=%s",
      sThreadMgr.get(), sClientId, sDisplayAttrMgr.get(),
      sCategoryMgr.get(), sDisabledDocumentMgr.get(), sDisabledContext.get(),
      GetBoolName(sCreateNativeCaretForLegacyATOK),
+     GetBoolName(sDoNotReturnNoLayoutErrorToATOKOfCompositionString),
      GetBoolName(sDoNotReturnNoLayoutErrorToFreeChangJie),
      GetBoolName(sDoNotReturnNoLayoutErrorToEasyChangjei),
      GetBoolName(sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtFirstChar),
      GetBoolName(sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtCaret)));
 }
 
 // static
 void

--- a/widget/windows/TSFTextStore.h
+++ b/widget/windows/TSFTextStore.h
@@ -981,16 +981,17 @@ protected:
 
   static StaticRefPtr<ITfInputProcessorProfiles> sInputProcessorProfiles;
 
   // TSF client ID for the current application
   static DWORD sClientId;
 
   // Enables/Disables hack for specific TIP.
   static bool sCreateNativeCaretForLegacyATOK;
+  static bool sDoNotReturnNoLayoutErrorToATOKOfCompositionString;
   static bool sDoNotReturnNoLayoutErrorToMSSimplifiedTIP;
   static bool sDoNotReturnNoLayoutErrorToMSTraditionalTIP;
   static bool sDoNotReturnNoLayoutErrorToFreeChangJie;
   static bool sDoNotReturnNoLayoutErrorToEasyChangjei;
   static bool sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtFirstChar;
   static bool sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtCaret;
   static bool sHackQueryInsertForMSSimplifiedTIP;
   static bool sHackQueryInsertForMSTraditionalTIP;