They got caught out by Firefox's new way of handling extension preferences and A9 have moved to a webpage-based preference system. The odd thing is that all my other extensions (forecast fox, tabbrowser preferences, gmail notifier and chatzilla) have all coped perfectly well with the change and are still using dialog boxes for prefs and settings.
It looks like the A9 workaround is simply that, and hopefully they will return to a dialog box format in due course.
The other odd thing was that the fixed toolbar was not flagged for extension update. So any user who is checking for updates won't be aware that a fix is in place - to find it they need to visit http://toolbar.a9.com.
Thanks for the fix A9, now you can get to work on the rest of my wishlist ;-)