[byroot]

Browser marketshare is not a constant, it totally depends of your business. At my current job it's:

  - ~55% Chrome
  - ~35% Firefox
  - ~5% Safari
  - 1.5% IE 9+10
  - 1% Opera

So for us it make sense to use API even less supported than WebWorkers, like http://caniuse.com/pagevisibility

But if I was working for a chinese market place, or a bank intranet I'm sure it would be 80% IE6.