It's a great extension when you find a working version. You can follow the links from GetFarky.com to http://www.cogjam.com/svn/fark/farkit/dist/ for the latest version. The one called latest version still would not install on FF 3.01, but the one labeled Beta did.
This is an extremely useful extension, and I use it all the time. I've discovered, though, that it doesn't play well with the Farky extension (in this case, the latest version, 1.14e) in one specific case.
Farky, if the option is selected, puts an arrow next to forum posts with your Fark userid, alerting you when someone responds to one of your posts. If you try to use Farkit to quote text from one of those posts, it won't put anything in the reply box.
It works fine for other posts modified by Farky, the only ones that seem not to work are the ones that have the arrow next to them indicating that someone has replied to you.
Thank you for updating this! I really missed it!