now it works well on non-Webkit/Blink browsers

document.body.scrollTop returns 0 on Firefox, making the popover open in a incorrect Y value.

I used a hack to put the correct code on non-Webkit/Blink browsers:
http://browserhacks.com

http://stackoverflow.com/questions/7435843/window-top-document-body-scrolltop-not-working-in-chrome-or-firefox
http://stackoverflow.com/questions/12941150/scrolltop-returns-0-in-firefox-but-not-in-chrome

Google Chrome 38
![Google Chrome 38](https://cloud.githubusercontent.com/assets/463661/4435293/47b2f7c6-473d-11e4-996a-a4a188ab0e06.png)

Firefox 32.0.3
![Firefox 32.0.3](https://cloud.githubusercontent.com/assets/463661/4435292/47af61d8-473d-11e4-9b91-fec0740f4e49.png)