I'm having problems trying to get my userContent.css to work in Firefox 23

I'm having problems trying to get my userContent.css to work in Firefox 23

I've got a simple chrome/userContent.css in my profile:
% cat ~/Library/Application\
Support/Firefox/Profiles/7h7pwntq.default/chrome/userContent.css
@-moz-document domain(reddit.com) {
textarea {
font-family: Monaco, monospace;
}
}
%
But it doesn't seem to be working. I'm sure this is the right profile
directory (it's the only one), and I've tried reloading pages and
restarting Firefox to no effect.
What am I doing wrong?