The chat is pretty great. But it has an obscure and frustrating phenomenon. When I get pinged, the message gets highlighted, which shoves the icons over to the left a little for some reason.
Since I'll very often want to reply to a message that pings me, I'll move my mouse to that reply icon...
... and it just so happens that the amount of time it takes to position my mouse on that small icon is the same amount of time it takes for the highlight to end, so the margins shift over to the right again just when I'm ready to click.
This line of CSS appears to be the troublemaker:
With it disabled, I think the phenomenon would disappear.
(I'm using Firefox 26.)