Nevermind, I figured out what it was.

I had originally titled a post about last weekend "''I'm tryin' ta think, but nuttin' happens!'' --Curly, The Three Stooges", but a bit of poking around inside the index file generated by my weblogging application revealed that putting a pair of dashes into the title of a post does something that HTML4 doesn't expect - it thinks that they either start or end a comment in a block of HTML. Carefully looking at the frontpage, I could see where the string of posts was broken because there was a post, then part of a post without the headers, then another part of a post without the headers, and then plain HTML text for the rest of the page, and nothing else. If there are no tags that suggest that something is a comment, (like <-- or >--) at least Firefox will barf and go nondeterministic, thus breaking the page. It stopped trying to use the CSS settings when it got to the b0rken wannabe HTML tag.

Note to self: Don't use my usual double-dash character string to credit a quote in the titles of my posts.

I'm going to bed.