Indent/un-indent not working

Hi,

I'm having trouble figuring out in what circumstances the indent/non-indent buttons are usable. They always appear unavailable when I'm creating either a bulleted or a numbered list. Even when I highlight a list item, they aren't available. I can indent without the buttons by hitting "tab", but there doesn't seem to be a way to un-indent, short of going into the HTML. I've tried both Safari and Firefox on a Mac.

Thanks!