(FMX) pre-loader help

hi everyone!

how its done, when you enter to site http://www.calpoly.edu/~mghanson/flash/spacegrid.html pre-loader loading the content of site
and when you re-enter to site you see the
pre-loader once again and pre-loader loading from 1 to 100 fast
what script cause this effect ?

i have 2 mc, mc1 with script :

onClipEvent (enterFrame) {
if (!loaded && this._url != _root._url) {
if (this.getBytesLoaded() == this.getBytesTotal()) {
loaded = true;
_root.mc2.gotoAndPlay(“preloader”);
}
}
}

and mc2 have preloader in 2 frames and then goes frame with label loadMovie(“content”)

but its not working, help me pls…