--- a/dom/events/ContentEventHandler.cpp
+++ b/dom/events/ContentEventHandler.cpp
@@ -1422,17 +1422,16 @@ ContentEventHandler::OnQueryTextRectArra
     return rv;
   }
 
   LineBreakType lineBreakType = GetLineBreakType(aEvent);
   RefPtr<nsRange> range = new nsRange(mRootContent);
   uint32_t offset = aEvent->mInput.mOffset;
 
   LayoutDeviceIntRect rect;
-  WritingMode writingMode;
   while (aEvent->mInput.mLength > aEvent->mReply.mRectArray.Length()) {
     rv = SetRangeFromFlatTextOffset(range, offset, 1, lineBreakType, true,
                                     nullptr);
     if (NS_WARN_IF(NS_FAILED(rv))) {
       return rv;
     }
 
     // get the starting frame
@@ -1461,16 +1460,20 @@ ContentEventHandler::OnQueryTextRectArra
     for (size_t i = 0; i < charRects.Length(); i++) {
       nsRect charRect = charRects[i];
       charRect.x += frameRect.x;
       charRect.y += frameRect.y;
 
       rect = LayoutDeviceIntRect::FromUnknownRect(
                charRect.ToOutsidePixels(mPresContext->AppUnitsPerDevPixel()));
 
+      // Ensure at least 1px width and height for avoiding empty rect.
+      rect.height = std::max(1, rect.height);
+      rect.width = std::max(1, rect.width);
+
       aEvent->mReply.mRectArray.AppendElement(rect);
     }
     offset += charRects.Length();
   }
   aEvent->mSucceeded = true;
   return NS_OK;
 }