According to this blog entry, you should be able to look words up in Bluefire.
I have v1.9, which I assume includes the updates from the version mentioned in the blog post above, 1.8, and I cannot figure out how to get the definition of a word. Highlighting it just brings up Highlight|Note. I am connected to the internet, so the lookup to Google shouldn't be a problem. I checked all the settings screens and none have anything related to dictionaries.
Anyone know how it works?