EDIT: nope, I am not using NoScript and am also not seeing jQuery effects. It's not blocked. Everything worked well in Firefox 3.6 before I updated.
EDIT 2: AdBlock was the culprit. Updating AdBlock fixes it.
EDIT 3: Nope, not Adblock. Not any of the extensions (uninstalled everything, not just disabled). It's an intermittent problem. Sometimes it will show the red bar, but refreshing the page will fix it. Other times refreshing it won't fix it at all. Usually it works. Looks like a bug.