In tab "Page 1" there is supposed to be a Java Applet running. The applet is from this page: Life Cycle of an Applet.

Tab "Page 2" contains just some dummy text so that you can switch to it.

In Firefox 3.6.8 on Windows 7 x64 (with 32-bit JRE) the applet will quite often (almost always) not load properly, and if you switch tabs the applet will be completely unloaded and reload, making it lose any instance state it has. On IE8 on the same machine the applet seems to operate as it should. Going into the Java Control Panel -> Advanced -> Debugging and enabling all the three debugging options should give you full life-cycle feedback of the applet in the Java Plugin console (I believe a full browser restart is required to activate it).