On further testing, with SeaMonkey (on my Windows 11 laptop): The scrollbar works fine in this thread. On going to The Spotted Thread, which has large inline pix, it seems to sometimes work and sometimes disappear. When it disappears the thread page never finishes loading, even though everything on the page appears to have loaded, including the pix, and I'm looking at the last post in the thread like nothing is wrong or different, just no scrollbar. If the the thread page finishes loading, the scrollbar works. Again, that's with SeaMonkey. Firefox has no trouble.