The Desktop Looked Right: 2,093 Parse Errors a Boot, and 10.9 Seconds That Weren't Doing Anything

A Debian desktop that looked and behaved correctly was throwing 2,093 CSS parse errors per boot and spending 10.9 seconds of a 39-second boot waiting on nothing. Neither is visible on screen. Both are in the journal, and both were introduced by the script that was supposed to set the machine up.