Hello. I was wondering if anyone knew of an add-on (preferably for Firefox) that's similar to Rikaichan, but instead of providing English translations for JP words it provides a Japanese definition.

Like... Instead of
弁明 - "explanation; excuse; vindication; apology;"
it'd say something like
弁明 - "事情などを説明してはっきりさせること。「事のやむなきを―する」" <- from dictionary.goo.ne.jp

... Yup.