I installed the 'destroy the web!' add-on yesterday to my firefox browser, and it was all working fine- today, having done nothing to change my browser or anything, it's suddenly not working. The logo button is still on the browser next to the address bar, but nothing happens when I click it to start a game, as if it's not even there?
If you go to Tools - Web Developer - Error Console, are there any errors reported?
Also, you can try to uninstall and then reinstall the latest version of Destroy the Web. Sorry for the inconvenience.