You want to run a Java application in your web browser Firefox (typically a webinar), you need a Java plugin installed ! Here's how to do it, in Ubuntu 12.04.
Installing, a Firefox Java plugin, could be a little difficult : since Open JDK is the favoured Java implementation in Ubuntu. there's not much information about installing the Java plugin. Moreover, the plugin is not found by the browser, when it tries to install it.
In fact, it's quite simple, you only need to install the package icedtea-plugin !
Happy Javan in Firefox.