This happened in one of my posts about a week ago. In my case, chipmunk came in and fixed all the HTML-ized ampersands in my code. That post was in Obfuscation, if it makes a difference in tracking the problem down.

Update: At the request of a senior monk, I add the fact that my problem occured using Mozilla 0.81 on RedHat Linux 7.1. I had assumed it was a Mozilla fluke until I saw this thread.

Experiment: &&  || [] (Typed two ampersands, two pipes, and open/close brackets.) Now it seems to work.