--- a/widget/windows/TSFTextStore.cpp
+++ b/widget/windows/TSFTextStore.cpp
@@ -1179,17 +1179,17 @@ bool TSFTextStore::sHackQueryInsertForMS
 #define TEXTSTORE_DEFAULT_VIEW (1)
 
 TSFTextStore::TSFTextStore()
   : mEditCookie(0)
   , mSinkMask(0)
   , mLock(0)
   , mLockQueued(0)
   , mHandlingKeyMessage(0)
-  , mLockedContent(mComposition, mSelection)
+  , mContentForTSF(mComposition, mSelection)
   , mRequestedAttrValues(false)
   , mIsRecordingActionsWithoutLock(false)
   , mPendingOnSelectionChange(false)
   , mHasReturnedNoLayoutError(false)
   , mWaitingQueryLayout(false)
   , mPendingDestroy(false)
   , mDeferClearingLockedContent(false)
   , mNativeCaretIsCreated(false)
@@ -1490,17 +1490,17 @@ TSFTextStore::RequestLock(DWORD dwLockFl
 
   if (!mSink) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("TSF: 0x%p   TSFTextStore::RequestLock() FAILED due to "
        "any sink not stored", this));
     return E_FAIL;
   }
   if (mDestroyed &&
-      (!mLockedContent.IsInitialized() || mSelection.IsDirty())) {
+      (!mContentForTSF.IsInitialized() || mSelection.IsDirty())) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("TSF: 0x%p   TSFTextStore::RequestLock() FAILED due to "
        "being destroyed and no information of the contents", this));
     return E_FAIL;
   }
   if (!phrSession) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("TSF: 0x%p   TSFTextStore::RequestLock() FAILED due to "
@@ -1832,21 +1832,21 @@ TSFTextStore::MaybeFlushPendingNotificat
     // If it's already been destroyed completely, this shouldn't notify TSF of
     // anything anymore.
     MOZ_LOG(sTextStoreLog, LogLevel::Debug,
       ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
        "does nothing because this has already destroyed completely...", this));
     return;
   }
 
-  if (!mDeferClearingLockedContent && mLockedContent.IsInitialized()) {
-    mLockedContent.Clear();
+  if (!mDeferClearingLockedContent && mContentForTSF.IsInitialized()) {
+    mContentForTSF.Clear();
     MOZ_LOG(sTextStoreLog, LogLevel::Debug,
            ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
-            "mLockedContent is cleared", this));
+            "mContentForTSF is cleared", this));
   }
 
   if (mHasReturnedNoLayoutError) {
     MOZ_LOG(sTextStoreLog, LogLevel::Info,
            ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
             "calling TSFTextStore::NotifyTSFOfLayoutChange()...", this));
     NotifyTSFOfLayoutChange();
   }
@@ -1977,74 +1977,74 @@ TSFTextStore::GetSelection(ULONG ulIndex
   return S_OK;
 }
 
 TSFTextStore::Content&
 TSFTextStore::LockedContent()
 {
   // This should be called when the document is locked or the content hasn't
   // been abandoned yet.
-  if (NS_WARN_IF(!IsReadLocked() && !mLockedContent.IsInitialized())) {
+  if (NS_WARN_IF(!IsReadLocked() && !mContentForTSF.IsInitialized())) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
            ("TSF: 0x%p   TSFTextStore::LockedContent(), FAILED, due to "
             "called wrong timing, IsReadLocked()=%s, "
-            "mLockedContent.IsInitialized()=%s",
+            "mContentForTSF.IsInitialized()=%s",
             this, GetBoolName(IsReadLocked()),
-            GetBoolName(mLockedContent.IsInitialized())));
-    mLockedContent.Clear();
-    return mLockedContent;
+            GetBoolName(mContentForTSF.IsInitialized())));
+    mContentForTSF.Clear();
+    return mContentForTSF;
   }
 
   Selection& currentSel = CurrentSelection();
   if (currentSel.IsDirty()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
            ("TSF: 0x%p   TSFTextStore::LockedContent(), FAILED, due to "
             "CurrentSelection() failure", this));
-    mLockedContent.Clear();
-    return mLockedContent;
-  }
-
-  if (!mLockedContent.IsInitialized()) {
+    mContentForTSF.Clear();
+    return mContentForTSF;
+  }
+
+  if (!mContentForTSF.IsInitialized()) {
     nsAutoString text;
     if (NS_WARN_IF(!GetCurrentText(text))) {
       MOZ_LOG(sTextStoreLog, LogLevel::Error,
              ("TSF: 0x%p   TSFTextStore::LockedContent(), FAILED, due to "
               "GetCurrentText() failure", this));
-      mLockedContent.Clear();
-      return mLockedContent;
+      mContentForTSF.Clear();
+      return mContentForTSF;
     }
 
-    mLockedContent.Init(text);
+    mContentForTSF.Init(text);
     // Basically, the locked content should be cleared after the document is
     // unlocked.  However, in e10s mode, content will be modified
     // asynchronously.  In such case, mDeferClearingLockedContent may be
     // true even after the document is unlocked.
     mDeferClearingLockedContent = false;
   }
 
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
          ("TSF: 0x%p   TSFTextStore::LockedContent(): "
-          "mLockedContent={ mText=\"%s\" (Length()=%u), "
+          "mContentForTSF={ mText=\"%s\" (Length()=%u), "
           "mLastCompositionString=\"%s\" (Length()=%u), "
           "mMinTextModifiedOffset=%u }",
-          this, mLockedContent.Text().Length() <= 20 ?
-            NS_ConvertUTF16toUTF8(mLockedContent.Text()).get() : "<omitted>",
-          mLockedContent.Text().Length(),
-          NS_ConvertUTF16toUTF8(mLockedContent.LastCompositionString()).get(),
-          mLockedContent.LastCompositionString().Length(),
-          mLockedContent.MinTextModifiedOffset()));
-
-  return mLockedContent;
+          this, mContentForTSF.Text().Length() <= 20 ?
+            NS_ConvertUTF16toUTF8(mContentForTSF.Text()).get() : "<omitted>",
+          mContentForTSF.Text().Length(),
+          NS_ConvertUTF16toUTF8(mContentForTSF.LastCompositionString()).get(),
+          mContentForTSF.LastCompositionString().Length(),
+          mContentForTSF.MinTextModifiedOffset()));
+
+  return mContentForTSF;
 }
 
 bool
 TSFTextStore::GetCurrentText(nsAString& aTextContent)
 {
-  if (mLockedContent.IsInitialized()) {
-    aTextContent = mLockedContent.Text();
+  if (mContentForTSF.IsInitialized()) {
+    aTextContent = mContentForTSF.Text();
     return true;
   }
 
   MOZ_ASSERT(!mDestroyed);
   MOZ_ASSERT(mWidget && !mWidget->Destroyed());
 
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
          ("TSF: 0x%p   TSFTextStore::GetCurrentText(): "
@@ -3320,17 +3320,17 @@ TSFTextStore::GetACPFromPoint(TsViewCook
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
            ("TSF: 0x%p   TSFTextStore::GetACPFromPoint() FAILED due to "
             "null pacp", this));
     return E_INVALIDARG;
   }
 
   mWaitingQueryLayout = false;
 
-  if (mDestroyed || mLockedContent.IsLayoutChanged()) {
+  if (mDestroyed || mContentForTSF.IsLayoutChanged()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
            ("TSF: 0x%p   TSFTextStore::GetACPFromPoint() returned "
             "TS_E_NOLAYOUT", this));
     mHasReturnedNoLayoutError = true;
     return TS_E_NOLAYOUT;
   }
 
   LayoutDeviceIntPoint ourPt(pt->x, pt->y);
@@ -3480,17 +3480,17 @@ TSFTextStore::GetTextExt(TsViewCookie vc
   mWaitingQueryLayout = false;
 
   // NOTE: TSF (at least on Win 8.1) doesn't return TS_E_NOLAYOUT to the
   // caller even if we return it.  It's converted to just E_FAIL.
   // However, this is fixed on Win 10.
 
   const TSFStaticSink* kSink = TSFStaticSink::GetInstance();
   if (mComposition.IsComposing() && mComposition.mStart < acpEnd &&
-      mLockedContent.IsLayoutChangedAfter(acpEnd)) {
+      mContentForTSF.IsLayoutChangedAfter(acpEnd)) {
     const Selection& currentSel = CurrentSelection();
     // The bug of Microsoft Office IME 2010 for Japanese is similar to
     // MS-IME for Win 8.1 and Win 10.  Newer version of MS Office IME is not
     // released yet.  So, we can hack it without prefs  because there must be
     // no developers who want to disable this hack for tests.
     const bool kIsMSOfficeJapaneseIME2010 =
       kSink->IsMSOfficeJapaneseIME2010Active();
     // MS IME for Japanese doesn't support asynchronous handling at deciding
@@ -3504,34 +3504,34 @@ TSFTextStore::GetTextExt(TsViewCookie vc
          kSink->IsMSJapaneseIMEActive())) {
       // Basically, MS-IME tries to retrieve whole composition string rect
       // at deciding suggest window immediately after unlocking the document.
       // However, in e10s mode, the content hasn't updated yet in most cases.
       // Therefore, if the first character at the retrieving range rect is
       // available, we should use it as the result.
       if ((kIsMSOfficeJapaneseIME2010 ||
            sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtFirstChar) &&
-          !mLockedContent.IsLayoutChangedAfter(acpStart) &&
+          !mContentForTSF.IsLayoutChangedAfter(acpStart) &&
           acpStart < acpEnd) {
         acpEnd = acpStart;
         MOZ_LOG(sTextStoreLog, LogLevel::Debug,
                ("TSF: 0x%p   TSFTextStore::GetTextExt() hacked the offsets "
                 "of the first character of changing range of the composition "
                 "string for TIP acpStart=%d, acpEnd=%d",
                 this, acpStart, acpEnd));
       }
       // Although, the condition is not clear, MS-IME sometimes retrieves the
       // caret rect immediately after modifying the composition string but
       // before unlocking the document.  In such case, we should return the
       // nearest character rect.
       else if ((kIsMSOfficeJapaneseIME2010 ||
                 sDoNotReturnNoLayoutErrorToMSJapaneseIMEAtCaret) &&
                acpStart == acpEnd &&
                currentSel.IsCollapsed() && currentSel.EndOffset() == acpEnd) {
-        acpEnd = acpStart = mLockedContent.MinOffsetOfLayoutChanged();
+        acpEnd = acpStart = mContentForTSF.MinOffsetOfLayoutChanged();
         MOZ_LOG(sTextStoreLog, LogLevel::Debug,
                ("TSF: 0x%p   TSFTextStore::GetTextExt() hacked the offsets "
                 "of the caret of the composition string for TIP acpStart=%d, "
                 "acpEnd=%d", this, acpStart, acpEnd));
       }
     }
     // Free ChangJie 2010 and Easy Changjei 1.0.12.0 doesn't handle
     // ITfContextView::GetTextExt() properly.  Prehaps, it's due to the bug of
@@ -3559,17 +3559,17 @@ TSFTextStore::GetTextExt(TsViewCookie vc
       acpEnd = mComposition.mStart;
       acpStart = std::min(acpStart, acpEnd);
       MOZ_LOG(sTextStoreLog, LogLevel::Debug,
              ("TSF: 0x%p   TSFTextStore::GetTextExt() hacked the offsets for "
               "TIP acpStart=%d, acpEnd=%d", this, acpStart, acpEnd));
     }
   }
 
-  if (mLockedContent.IsLayoutChangedAfter(acpEnd)) {
+  if (mContentForTSF.IsLayoutChangedAfter(acpEnd)) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
            ("TSF: 0x%p   TSFTextStore::GetTextExt() returned TS_E_NOLAYOUT "
             "(acpEnd=%d)", this, acpEnd));
     mHasReturnedNoLayoutError = true;
     return TS_E_NOLAYOUT;
   }
 
   if (mDestroyed) {
@@ -4842,20 +4842,20 @@ TSFTextStore::NotifyTSFOfLayoutChange()
 
   // If we returned TS_E_NOLAYOUT, TIP should query the computed layout again.
   mWaitingQueryLayout = returnedNoLayoutError;
 
   // For avoiding to call this method again at unlocking the document during
   // calls of OnLayoutChange(), reset mHasReturnedNoLayoutError.
   mHasReturnedNoLayoutError = false;
 
-  // Now, layout has been computed.  We should notify mLockedContent for
+  // Now, layout has been computed.  We should notify mContentForTSF for
   // making GetTextExt() and GetACPFromPoint() not return TS_E_NOLAYOUT.
-  if (mLockedContent.IsInitialized()) {
-    mLockedContent.OnLayoutChanged();
+  if (mContentForTSF.IsInitialized()) {
+    mContentForTSF.OnLayoutChanged();
   }
 
   // Now, the caret position is different from ours.  Destroy the native caret
   // if there is.
   MaybeDestroyNativeCaret();
 
   // This method should return true if either way succeeds.
   bool ret = true;

--- a/widget/windows/TSFTextStore.h
+++ b/widget/windows/TSFTextStore.h
@@ -780,28 +780,29 @@ protected:
     enum : uint32_t
     {
       NOT_MODIFIED = UINT32_MAX
     };
     uint32_t mMinTextModifiedOffset;
 
     bool mInitialized;
   };
-  // mLockedContent starts to cache content of the document at first query of
-  // the content during a document lock.  This is abandoned after document is
-  // unlocked and dispatched events are handled.  This is initialized by
-  // LockedContent() automatically.  So, don't access this member directly
-  // except at calling Clear(), IsInitialized(), IsLayoutChangedAfter() or
-  // IsLayoutChanged().
-  Content mLockedContent;
+  // mContentForTSF starts to cache content of the document at first query of
+  // the content during a document lock.  The information is expected by TSF
+  // and TIP.  Therefore, this is useful for answering the query from TSF or
+  // TIP.  This is abandoned after document is unlocked and dispatched events
+  // are handled.  This is initialized by LockedContent() automatically.
+  // So, don't access this member directly except at calling Clear(),
+  // IsInitialized(), IsLayoutChangedAfter() or IsLayoutChanged().
+  Content mContentForTSF;
 
   Content& LockedContent();
 
   // While the documet is locked, this returns the text stored by
-  // mLockedContent.  Otherwise, return the current text content.
+  // mContentForTSF.  Otherwise, return the current text content.
   bool GetCurrentText(nsAString& aTextContent);
 
   class MouseTracker final
   {
   public:
     static const DWORD kInvalidCookie = static_cast<DWORD>(-1);
 
     MouseTracker();
@@ -879,17 +880,17 @@ protected:
   // ITfContextOwnerServices::OnLayoutChange(), mWaitingQueryLayout is set to
   // true.  This is set to  false when GetTextExt() or GetACPFromPoint() is
   // called.
   bool                         mWaitingQueryLayout;
   // During the documet is locked, we shouldn't destroy the instance.
   // If this is true, the instance will be destroyed after unlocked.
   bool                         mPendingDestroy;
   // If this is false, MaybeFlushPendingNotifications() will clear the
-  // mLockedContent.
+  // mContentForTSF.
   bool                         mDeferClearingLockedContent;
   // While there is native caret, this is true.  Otherwise, false.
   bool                         mNativeCaretIsCreated;
   // While the instance is dispatching events, the event may not be handled
   // synchronously in e10s mode.  So, in such case, in strictly speaking,
   // we shouldn't query layout information.  However, TS_E_NOLAYOUT bugs of
   // ITextStoreAPC::GetTextExt() blocks us to behave ideally.
   // For preventing it to be called, we should put off notifying TSF of