What processing/rendering *don't* browsers do while a tab doesn't have focus?
<p>I've got a page that shows real-time statistics. It runs a lot of javascript, makes a lot of HTTP requests, renders SVG charts every few seconds using D3.js, has a lot of CSS animations, and rearranges the DOM frequently.</p>

<p>As long as the page is focused, it runs smoothly. If I switch to another tab and come back later, there's often a short pause where the page seems to be frozen before the view suddenly seems to rerender and the page becomes usable again. The longer the tab has been backgrounded, the longer this pause is. If the tab has been in the background for a very long time (hours) and I switch back to it, it will be frozen for a long time then crash.</p>

<p>All these behaviors are observed in Chrome. I haven't tested much in other browsers.</p>

<p>What is Chrome doing during that pause when I first switch back to the tab?</p>
