[01/26/2007] The Firefox extension is now available for download. It's nowhere near complete yet, but it does have the Acceptance-Fitnesse format to get you started.
[01/19/2007] We have a proof of concept working. I'm using it for a project here and it works fine. Now to productize it..
Get started using Tk-Acceptance
I'm working on a screencast that should make it easier for you to set up acceptance into your own project.