We've decided to update XKit. It's harder than it looks. We're not in contact with the original XKit Guy, nor do we have access to xkit.info. We currently operate at this blog and on GitHub.
Firefox keeps saying xkit is non-compatable. Am I doing something wrong?
I might be wrong in my previous answer, then. If you’re using an older version it may happen that this occurs, and the only way to fix it to get Firefox up-to-date.