Like Ron, I suspect that the problem is related to Firefox 12 but probably because people submitting answers are having problems with it.
When a FF12 user submits an answer they don't immediately see it. (They need to refresh the page in order for it to show up). That can result in people thinking that AB's server hasn't accepted their post, so they re-post their reply. When an identical reply is posted, AB's system increases the answer count but deletes the duplicate post, resulting in the counter showing more posts than there really are.
Chris