overlay is not removed in firefox 42/43

it seems that the loader finished its work slower in firefox (half a second slower? maybe it has something to do with loading-line fading out), and missed the chance to remove the `qLtempOverlay` overlay div.

```
onComplete: function(){
//fix firefox bug
if(navigator.userAgent.indexOf('Firefox') !== -1){
$('#qLtempOverlay').remove();
}
}
```

tested on firefox 42/43

ps, in my case, the `queryloader2.min.js` script is loaded via `$.getScript()`.