--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -3262,17 +3262,28 @@ IMEInputHandler::GetAttributedSubstringF
          "computed with mIMECompositionString (result string=\"%s\")",
          this, NS_ConvertUTF16toUTF8(str).get()));
     }
     return result;
   }
 
   nsAutoString str;
   WidgetQueryContentEvent textContent(true, eQueryTextContent, mWidget);
-  textContent.InitForQueryTextContent(aRange.location, aRange.length);
+  WidgetQueryContentEvent::Options options;
+  int64_t startOffset = aRange.location;
+  if (IsIMEComposing()) {
+    // The composition may be at different offset from the selection start
+    // offset at dispatching compositionstart because start of composition
+    // is fixed when composition string becomes non-empty in the editor.
+    // Therefore, we need to use query event which is relative to insertion
+    // point.
+    options.mRelativeToInsertionPoint = true;
+    startOffset -= mIMECompositionStart;
+  }
+  textContent.InitForQueryTextContent(startOffset, aRange.length, options);
   textContent.RequestFontRanges();
   DispatchEvent(textContent);
 
   MOZ_LOG(gLog, LogLevel::Info,
     ("%p IMEInputHandler::GetAttributedSubstringFromRange, "
      "textContent={ mSucceeded=%s, mReply={ mString=\"%s\", mOffset=%llu } }",
      this, TrueOrFalse(textContent.mSucceeded),
      NS_ConvertUTF16toUTF8(textContent.mReply.mString).get(),
@@ -3430,32 +3441,54 @@ IMEInputHandler::FirstRectForCharacterRa
   }
 
   RefPtr<IMEInputHandler> kungFuDeathGrip(this);
 
   LayoutDeviceIntRect r;
   bool useCaretRect = (aRange.length == 0);
   if (!useCaretRect) {
     WidgetQueryContentEvent charRect(true, eQueryTextRect, mWidget);
-    charRect.InitForQueryTextRect(aRange.location, 1);
+    WidgetQueryContentEvent::Options options;
+    int64_t startOffset = aRange.location;
+    if (IsIMEComposing()) {
+      // The composition may be at different offset from the selection start
+      // offset at dispatching compositionstart because start of composition
+      // is fixed when composition string becomes non-empty in the editor.
+      // Therefore, we need to use query event which is relative to insertion
+      // point.
+      options.mRelativeToInsertionPoint = true;
+      startOffset -= mIMECompositionStart;
+    }
+    charRect.InitForQueryTextRect(startOffset, 1, options);
     DispatchEvent(charRect);
     if (charRect.mSucceeded) {
       r = charRect.mReply.mRect;
       actualRange.location = charRect.mReply.mOffset;
       actualRange.length = charRect.mReply.mString.Length();
       mWritingMode = charRect.GetWritingMode();
       mRangeForWritingMode = actualRange;
     } else {
       useCaretRect = true;
     }
   }
 
   if (useCaretRect) {
     WidgetQueryContentEvent caretRect(true, eQueryCaretRect, mWidget);
-    caretRect.InitForQueryCaretRect(aRange.location);
+    WidgetQueryContentEvent::Options options;
+    int64_t startOffset = aRange.location;
+    if (IsIMEComposing()) {
+      // The composition may be at different offset from the selection start
+      // offset at dispatching compositionstart because start of composition
+      // is fixed when composition string becomes non-empty in the editor.
+      // Therefore, we need to use query event which is relative to insertion
+      // point.
+      options.mRelativeToInsertionPoint = true;
+      startOffset -= mIMECompositionStart;
+    }
+    caretRect.InitForQueryCaretRect(startOffset, options);
     DispatchEvent(caretRect);
     if (!caretRect.mSucceeded) {
       return rect;
     }
     r = caretRect.mReply.mRect;
     r.width = 0;
     actualRange.location = caretRect.mReply.mOffset;
     actualRange.length = 0;