Jeff Johnson:

The madness in this case is Safari background tabs spontaneously coming to the front again, an obviously undesirable behavior.

Read the blog post for the specifics on what causes this (props to Jeff for figuring it out). To give this a try, follow the headline link, click the “Start 5 second timer” button, then click another tab to bring it to the front. After 5 seconds, the background tab will jump to the front. Works every time.

Turns into an ad for the highly regarded StopTheMadness browser extension. Worth a look.