This nifty utility extension gives you the ability to input Twitch and BetterTTV emotes into rabb.it chat. The emotes will be replaced by the links to the emote images hosted on twitchemotes.com.
There are 3 sizes to an emote: small, medium, and large.
To specify the size, put a number from 1 to 3 at the end.
WITH CUSTOM SIZE: ":emote:3"