I've released a new version of Windows HotPot that doesn't have that popup line in the source file. I'd recommend downloading the new version (hotpot.uvic.ca). Stewart should be releasing an updated Java version soon, if he hasn't done so already.
Our apologies for the confusion this has caused. The change in Firefox 17 took me by surprise, and to be honest, that browser message should have been removed years ago, because it's not really likely to be useful nowadays.
Cheers,
Martin