Hi, I expreriense the same problem. Under IE and Chrome it works fine but in Firefox it shows all of the content of the tabs under the first tab and the rest are inactive. I’m running on Windows 7, Firefox 27.0.1.
This problem appears especially when the names of the tabs are with cyrilic letters. The website for what I am using the plugin is in Bulgarian. When I use latin letters, the plugin works as a charm.