Thanks Kim - the FF24 hook dll was certainly what was needed, and FF now seems functional again.
However, problems persist in Chrome and IE - but I'm not necessarily convinced that it is purely a problem with TC....
Trying to start Chrome with TC doesn't even start Chrome, let alone navigate to the specified page.
Trying to start IE with TC starts IE, but doesn't navigate - the reason I don't think it's a TC fault is that I've rolled IE back to IE8 - and the problem persists... and I suspect SmartBear would have got TC working with IE8 by now ;-)
BTW I'm sure Chrome was only listed as supported up to 28 on the Smartbear site earlier ;-)
Any other pointers as to what might be the problem?