1. Open your browser (say to this forum). Tap and hold a (thread) link. Drag towards edge/bottom and drop when you see multi window outline. (Similar to dragging app icon from side panel to open multi window)
2. Now you have 2 browser instances opened side by side. (Just repeat if you need more instance)
3. Now you keep dragging link from first window and drop it to second window. The dropped link will open up in second window.
4. Now you have a parent-child windows surfing.