Yesterday in pursuing a query with Apple about the new Apple Watch products, I created a thread in Apple Community forum and saw what I thought was a very neat and effective way of trying to keep long threads focussed on the original topic.
Once a poster scrolls past the OP, a drop-down dismissable (click the "X" highlighted by the red arrow) pop-up window follows the scrolling activity while remaining anchored to the top of the browser window. The red box is the window with the thread title/topic.