--- a/widget/ContentCache.cpp
+++ b/widget/ContentCache.cpp
@@ -64,16 +64,44 @@ public:
       Assign("Vertical (LTR)");
       return;
     }
     Assign("Vertical (RTL)");
   }
   virtual ~GetWritingModeName() {}
 };
 
+class GetEscapedUTF8String final : public NS_ConvertUTF16toUTF8
+{
+public:
+  explicit GetEscapedUTF8String(const nsAString& aString)
+    : NS_ConvertUTF16toUTF8(aString)
+  {
+    Escape();
+  }
+  explicit GetEscapedUTF8String(const char16ptr_t aString)
+    : NS_ConvertUTF16toUTF8(aString)
+  {
+    Escape();
+  }
+  GetEscapedUTF8String(const char16ptr_t aString, uint32_t aLength)
+    : NS_ConvertUTF16toUTF8(aString, aLength)
+  {
+    Escape();
+  }
+
+private:
+  void Escape()
+  {
+    ReplaceSubstring("\r", "\\r");
+    ReplaceSubstring("\n", "\\n");
+    ReplaceSubstring("\t", "\\t");
+  }
+};
+
 /*****************************************************************************
  * mozilla::ContentCache
  *****************************************************************************/
 
 LazyLogModule sContentCacheLog("ContentCacheWidgets");
 
 ContentCache::ContentCache()
   : mCompositionStart(UINT32_MAX)
@@ -644,17 +672,17 @@ ContentCacheInParent::HandleQueryContent
       aEvent.mReply.mReversed = mSelection.Reversed();
       aEvent.mReply.mHasSelection = true;
       aEvent.mReply.mWritingMode = mSelection.mWritingMode;
       MOZ_LOG(sContentCacheLog, LogLevel::Info,
         ("0x%p HandleQueryContentEvent(), "
          "Succeeded, aEvent={ mReply={ mOffset=%u, mString=\"%s\", "
          "mReversed=%s, mHasSelection=%s, mWritingMode=%s } }",
          this, aEvent.mReply.mOffset,
-         NS_ConvertUTF16toUTF8(aEvent.mReply.mString).get(),
+         GetEscapedUTF8String(aEvent.mReply.mString).get(),
          GetBoolName(aEvent.mReply.mReversed),
          GetBoolName(aEvent.mReply.mHasSelection),
          GetWritingModeName(aEvent.mReply.mWritingMode).get()));
       break;
     case eQueryTextContent: {
       MOZ_LOG(sContentCacheLog, LogLevel::Info,
         ("0x%p HandleQueryContentEvent("
          "aEvent={ mMessage=eQueryTextContent, mInput={ mOffset=%u, "
@@ -732,17 +760,17 @@ ContentCacheInParent::HandleQueryContent
       aEvent.mReply.mOffset = aEvent.mInput.mOffset;
       // XXX This may be wrong if storing range isn't in the selection range.
       aEvent.mReply.mWritingMode = mSelection.mWritingMode;
       MOZ_LOG(sContentCacheLog, LogLevel::Info,
         ("0x%p HandleQueryContentEvent(), "
          "Succeeded, aEvent={ mReply={ mOffset=%u, mString=\"%s\", "
          "mWritingMode=%s, mRect=%s } }",
          this, aEvent.mReply.mOffset,
-         NS_ConvertUTF16toUTF8(aEvent.mReply.mString).get(),
+         GetEscapedUTF8String(aEvent.mReply.mString).get(),
          GetWritingModeName(aEvent.mReply.mWritingMode).get(),
          GetRectText(aEvent.mReply.mRect).get()));
       break;
     case eQueryCaretRect:
       MOZ_LOG(sContentCacheLog, LogLevel::Info,
         ("0x%p HandleQueryContentEvent("
          "aEvent={ mMessage=eQueryCaretRect, mInput={ mOffset=%u } }, "
          "aWidget=0x%p), mText.Length()=%u",
@@ -1018,17 +1046,17 @@ bool
 ContentCacheInParent::OnCompositionEvent(const WidgetCompositionEvent& aEvent)
 {
   MOZ_LOG(sContentCacheLog, LogLevel::Info,
     ("0x%p OnCompositionEvent(aEvent={ "
      "mMessage=%s, mData=\"%s\" (Length()=%u), mRanges->Length()=%u }), "
      "mPendingEventsNeedingAck=%u, mIsComposing=%s, "
      "mCommitStringByRequest=0x%p",
      this, ToChar(aEvent.mMessage),
-     NS_ConvertUTF16toUTF8(aEvent.mData).get(), aEvent.mData.Length(),
+     GetEscapedUTF8String(aEvent.mData).get(), aEvent.mData.Length(),
      aEvent.mRanges ? aEvent.mRanges->Length() : 0, mPendingEventsNeedingAck,
      GetBoolName(mIsComposing), mCommitStringByRequest));
 
   // We must be able to simulate the selection because
   // we might not receive selection updates in time
   if (!mIsComposing) {
     if (aEvent.mWidget && aEvent.mWidget->PluginHasFocus()) {
       // If focus is on plugin, we cannot get selection range

--- a/widget/windows/TSFTextStore.cpp
+++ b/widget/windows/TSFTextStore.cpp
@@ -658,16 +658,44 @@ public:
       AssignLiteral("Vertical (LR)");
       return;
     }
     AssignLiteral("Vertical (RL)");
   }
   virtual ~GetWritingModeName() {}
 };
 
+class GetEscapedUTF8String final : public NS_ConvertUTF16toUTF8
+{
+public:
+  explicit GetEscapedUTF8String(const nsAString& aString)
+    : NS_ConvertUTF16toUTF8(aString)
+  {
+    Escape();
+  }
+  explicit GetEscapedUTF8String(const char16ptr_t aString)
+    : NS_ConvertUTF16toUTF8(aString)
+  {
+    Escape();
+  }
+  GetEscapedUTF8String(const char16ptr_t aString, uint32_t aLength)
+    : NS_ConvertUTF16toUTF8(aString, aLength)
+  {
+    Escape();
+  }
+
+private:
+  void Escape()
+  {
+    ReplaceSubstring("\r", "\\r");
+    ReplaceSubstring("\n", "\\n");
+    ReplaceSubstring("\t", "\\t");
+  }
+};
+
 /******************************************************************/
 /* InputScopeImpl                                                 */
 /******************************************************************/
 
 class InputScopeImpl final : public ITfInputScope
 {
   ~InputScopeImpl() {}
 
@@ -1685,17 +1713,17 @@ TSFTextStore::FlushPendingActions()
         }
         break;
       }
       case PendingAction::COMPOSITION_UPDATE: {
         MOZ_LOG(sTextStoreLog, LogLevel::Debug,
           ("0x%p   TSFTextStore::FlushPendingActions() "
            "flushing COMPOSITION_UPDATE={ mData=\"%s\", "
            "mRanges=0x%p, mRanges->Length()=%d }",
-           this, NS_ConvertUTF16toUTF8(action.mData).get(),
+           this, GetEscapedUTF8String(action.mData).get(),
            action.mRanges.get(),
            action.mRanges ? action.mRanges->Length() : 0));
 
         // eCompositionChange causes a DOM text event, the IME will be notified
         // of NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED.  In this case, we
         // should not clear mContentForTSF until we notify the IME of the
         // composition update.
         mDeferClearingContentForTSF = true;
@@ -1727,17 +1755,17 @@ TSFTextStore::FlushPendingActions()
           // Be aware, the mWidget might already have been destroyed.
         }
         break;
       }
       case PendingAction::COMPOSITION_END: {
         MOZ_LOG(sTextStoreLog, LogLevel::Debug,
           ("0x%p   TSFTextStore::FlushPendingActions() "
            "flushing COMPOSITION_END={ mData=\"%s\" }",
-           this, NS_ConvertUTF16toUTF8(action.mData).get()));
+           this, GetEscapedUTF8String(action.mData).get()));
 
         // Dispatching eCompositionCommit causes a DOM text event, then,
         // the IME will be notified of NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED.
         // In this case, we should not clear mContentForTSFuntil we notify
         // the IME of the composition update.
         mDeferClearingContentForTSF = true;
 
         MOZ_LOG(sTextStoreLog, LogLevel::Debug,
@@ -2051,20 +2079,20 @@ TSFTextStore::ContentForTSFRef()
     mDeferClearingContentForTSF = false;
   }
 
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
     ("0x%p   TSFTextStore::ContentForTSFRef(): "
      "mContentForTSF={ mText=\"%s\" (Length()=%u), "
      "mLastCompositionString=\"%s\" (Length()=%u), "
      "mMinTextModifiedOffset=%u }",
-     this, mContentForTSF.Text().Length() <= 20 ?
-       NS_ConvertUTF16toUTF8(mContentForTSF.Text()).get() : "<omitted>",
+     this, mContentForTSF.Text().Length() <= 40 ?
+       GetEscapedUTF8String(mContentForTSF.Text()).get() : "<omitted>",
      mContentForTSF.Text().Length(),
-     NS_ConvertUTF16toUTF8(mContentForTSF.LastCompositionString()).get(),
+     GetEscapedUTF8String(mContentForTSF.LastCompositionString()).get(),
      mContentForTSF.LastCompositionString().Length(),
      mContentForTSF.MinTextModifiedOffset()));
 
   return mContentForTSF;
 }
 
 bool
 TSFTextStore::CanAccessActualContentDirectly() const
@@ -2473,17 +2501,17 @@ GetLineStyle(TF_DA_LINESTYLE aTSFLineSty
 HRESULT
 TSFTextStore::RecordCompositionUpdateAction()
 {
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
     ("0x%p   TSFTextStore::RecordCompositionUpdateAction(), "
      "mComposition={ mView=0x%p, mStart=%d, mString=\"%s\" "
      "(Length()=%d) }",
      this, mComposition.mView.get(), mComposition.mStart,
-     NS_ConvertUTF16toUTF8(mComposition.mString).get(),
+     GetEscapedUTF8String(mComposition.mString).get(),
      mComposition.mString.Length()));
 
   if (!mComposition.IsComposing()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("0x%p   TSFTextStore::RecordCompositionUpdateAction() FAILED "
        "due to no composition view", this));
     return E_FAIL;
   }
@@ -2949,17 +2977,17 @@ TSFTextStore::SetText(DWORD dwFlags,
   MOZ_LOG(sTextStoreLog, LogLevel::Info,
     ("0x%p TSFTextStore::SetText(dwFlags=%s, acpStart=%ld, "
      "acpEnd=%ld, pchText=0x%p \"%s\", cch=%lu, pChange=0x%p), "
      "mComposition.IsComposing()=%s",
      this, dwFlags == TS_ST_CORRECTION ? "TS_ST_CORRECTION" :
                                          "not-specified",
      acpStart, acpEnd, pchText,
      pchText && cch ?
-       NS_ConvertUTF16toUTF8(pchText, cch).get() : "",
+       GetEscapedUTF8String(pchText, cch).get() : "",
      cch, pChange, GetBoolName(mComposition.IsComposing())));
 
   // Per SDK documentation, and since we don't have better
   // ways to do this, this method acts as a helper to
   // call SetSelection followed by InsertTextAtSelection
   if (!IsReadWriteLocked()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("0x%p   TSFTextStore::SetText() FAILED due to "
@@ -3919,17 +3947,17 @@ TSFTextStore::InsertTextAtSelection(DWOR
   MOZ_LOG(sTextStoreLog, LogLevel::Info,
     ("0x%p TSFTextStore::InsertTextAtSelection(dwFlags=%s, "
      "pchText=0x%p \"%s\", cch=%lu, pacpStart=0x%p, pacpEnd=0x%p, "
      "pChange=0x%p), IsComposing()=%s",
      this, dwFlags == 0 ? "0" :
            dwFlags == TF_IAS_NOQUERY ? "TF_IAS_NOQUERY" :
            dwFlags == TF_IAS_QUERYONLY ? "TF_IAS_QUERYONLY" : "Unknown",
      pchText,
-     pchText && cch ? NS_ConvertUTF16toUTF8(pchText, cch).get() : "",
+     pchText && cch ? GetEscapedUTF8String(pchText, cch).get() : "",
      cch, pacpStart, pacpEnd, pChange,
      GetBoolName(mComposition.IsComposing())));
 
   if (cch && !pchText) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("0x%p   TSFTextStore::InsertTextAtSelection() FAILED due to "
        "null pchText", this));
     return E_INVALIDARG;
@@ -4015,17 +4043,17 @@ TSFTextStore::InsertTextAtSelection(DWOR
 
 bool
 TSFTextStore::InsertTextAtSelectionInternal(const nsAString& aInsertStr,
                                             TS_TEXTCHANGE* aTextChange)
 {
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
     ("0x%p   TSFTextStore::InsertTextAtSelectionInternal("
      "aInsertStr=\"%s\", aTextChange=0x%p), IsComposing=%s",
-     this, NS_ConvertUTF16toUTF8(aInsertStr).get(), aTextChange,
+     this, GetEscapedUTF8String(aInsertStr).get(), aTextChange,
      GetBoolName(mComposition.IsComposing())));
 
   Content& contentForTSF = ContentForTSFRef();
   if (!contentForTSF.IsInitialized()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("0x%p   TSFTextStore::InsertTextAtSelectionInternal() failed "
        "due to ContentForTSFRef() failure()", this));
     return false;
@@ -4048,17 +4076,17 @@ TSFTextStore::InsertTextAtSelectionInter
     MOZ_LOG(sTextStoreLog, LogLevel::Debug,
       ("0x%p   TSFTextStore::InsertTextAtSelectionInternal() "
        "appending pending compositionstart and compositionend... "
        "PendingCompositionStart={ mSelectionStart=%d, "
        "mSelectionLength=%d }, PendingCompositionEnd={ mData=\"%s\" "
        "(Length()=%u) }",
        this, compositionStart->mSelectionStart,
        compositionStart->mSelectionLength,
-       NS_ConvertUTF16toUTF8(compositionEnd->mData).get(),
+       GetEscapedUTF8String(compositionEnd->mData).get(),
        compositionEnd->mData.Length()));
   }
 
   contentForTSF.ReplaceSelectedTextWith(aInsertStr);
 
   if (aTextChange) {
     aTextChange->acpStart = oldSelection.acpStart;
     aTextChange->acpOldEnd = oldSelection.acpEnd;
@@ -4208,17 +4236,17 @@ TSFTextStore::RecordCompositionStartActi
 
 HRESULT
 TSFTextStore::RecordCompositionEndAction()
 {
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
     ("0x%p   TSFTextStore::RecordCompositionEndAction(), "
      "mComposition={ mView=0x%p, mString=\"%s\" }",
      this, mComposition.mView.get(),
-     NS_ConvertUTF16toUTF8(mComposition.mString).get()));
+     GetEscapedUTF8String(mComposition.mString).get()));
 
   MOZ_ASSERT(mComposition.IsComposing());
 
   CompleteLastActionIfStillIncomplete();
   PendingAction* action = mPendingActions.AppendElement();
   action->mType = PendingAction::COMPOSITION_END;
   action->mData = mComposition.mString;
 
@@ -4371,31 +4399,31 @@ TSFTextStore::OnUpdateComposition(ITfCom
          "SelectionForTSFRef() failure", this));
       return E_FAIL;
     }
     MOZ_LOG(sTextStoreLog, LogLevel::Info,
       ("0x%p   TSFTextStore::OnUpdateComposition() succeeded: "
        "mComposition={ mStart=%ld, mString=\"%s\" }, "
        "SelectionForTSFRef()={ acpStart=%ld, acpEnd=%ld, style.ase=%s }",
        this, mComposition.mStart,
-       NS_ConvertUTF16toUTF8(mComposition.mString).get(),
+       GetEscapedUTF8String(mComposition.mString).get(),
        selectionForTSF.StartOffset(), selectionForTSF.EndOffset(),
        GetActiveSelEndName(selectionForTSF.ActiveSelEnd())));
   }
   return S_OK;
 }
 
 STDMETHODIMP
 TSFTextStore::OnEndComposition(ITfCompositionView* pComposition)
 {
   MOZ_LOG(sTextStoreLog, LogLevel::Info,
     ("0x%p TSFTextStore::OnEndComposition(pComposition=0x%p), "
      "mComposition={ mView=0x%p, mString=\"%s\" }",
      this, pComposition, mComposition.mView.get(),
-     NS_ConvertUTF16toUTF8(mComposition.mString).get()));
+     GetEscapedUTF8String(mComposition.mString).get()));
 
   AutoPendingActionAndContentFlusher flusher(this);
 
   if (!mComposition.IsComposing()) {
     MOZ_LOG(sTextStoreLog, LogLevel::Error,
       ("0x%p   TSFTextStore::OnEndComposition() FAILED due to "
        "no active composition", this));
     return E_UNEXPECTED;
@@ -5235,17 +5263,17 @@ void
 TSFTextStore::CommitCompositionInternal(bool aDiscard)
 {
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
     ("0x%p   TSFTextStore::CommitCompositionInternal(aDiscard=%s), "
      "mSink=0x%p, mContext=0x%p, mComposition.mView=0x%p, "
      "mComposition.mString=\"%s\"",
      this, GetBoolName(aDiscard), mSink.get(), mContext.get(),
      mComposition.mView.get(),
-     NS_ConvertUTF16toUTF8(mComposition.mString).get()));
+     GetEscapedUTF8String(mComposition.mString).get()));
 
   // If the document is locked, TSF will fail to commit composition since
   // TSF needs another document lock.  So, let's put off the request.
   // Note that TextComposition will commit composition in the focused editor
   // with the latest composition string for web apps and waits asynchronous
   // committing messages.  Therefore, we can and need to perform this
   // asynchronously.
   if (IsReadLocked()) {
@@ -5860,19 +5888,19 @@ TSFTextStore::Content::ReplaceTextWith(L
         mMinTextModifiedOffset = firstDifferentOffset =
           mComposition.EndOffset();
       }
       MOZ_LOG(sTextStoreLog, LogLevel::Debug,
         ("0x%p   TSFTextStore::Content::ReplaceTextWith(aStart=%d, "
          "aLength=%d, aReplaceString=\"%s\"), mComposition={ mStart=%d, "
          "mString=\"%s\" }, mLastCompositionString=\"%s\", "
          "mMinTextModifiedOffset=%u, firstDifferentOffset=%u",
-         this, aStart, aLength, NS_ConvertUTF16toUTF8(aReplaceString).get(),
-         mComposition.mStart, NS_ConvertUTF16toUTF8(mComposition.mString).get(),
-         NS_ConvertUTF16toUTF8(mLastCompositionString).get(),
+         this, aStart, aLength, GetEscapedUTF8String(aReplaceString).get(),
+         mComposition.mStart, GetEscapedUTF8String(mComposition.mString).get(),
+         GetEscapedUTF8String(mLastCompositionString).get(),
          mMinTextModifiedOffset, firstDifferentOffset));
     } else {
       firstDifferentOffset =
         static_cast<uint32_t>(aStart) +
           FirstDifferentCharOffset(aReplaceString, replacedString);
     }
     mMinTextModifiedOffset =
       std::min(mMinTextModifiedOffset, firstDifferentOffset);