Hi all,
I've made a Chrome/Firefox extension which adds a row of buttons to the chat box for one-click sending of common messages (user definable). It's already available in the Chrome webstore, and it's been submitted to Mozilla Add-ons for review, so should be available for Firefox soon.
Any suggestions for improvement or bug reports are appreciated, and you can view the source on Github.
Edit: After a mere 6 weeks in the Firefox review queue, the Firefox version is here.