All /. articles that are colored green/teal have this problem: comment titles have white text on a white background, and thus are invisible. However, this occurs only when I'm logged in, not when I'm logged out.
This seems to be related to problem 2797951.
Apparently a different CSS loads when the user is logged in, and the title background color for the CSS comment class for green articles is undefined or invalid, so it defaults to white.
It's a serious problem that has forced me to log out permanently.
Context: Firefox 3.10 on Windows XP. I think it happens on Firefox 3.10 in OS X 10.5.7 too.