Screen artifacts after upgrading to WP 3.3.1

I just upgraded two sites to WP 3.3.1 and now have the same artifact showing up on both sites. One one site, it’s a large rectangular box on a post (theme: Newsport) https://llmultimedia.com/2010/07/18/your-family-tree/. On the other site it’s two boxes stuck together, like a table, on two of the pages (theme: Atahualpa) https://storiesfromthefield.org/2006-festival/. Other posts and pages on both sites are fine.

When I use Firebug, I can locate the line of code and delete it, which solves the problem in rehearsal, but of course those Firebug corrections can’t be saved (or at least I don’t know how they can). I don’t know how to get to the code and correct it for real. Can anyone help?