Firefox gets hung-up on external rollover "loadMovie" jpgs

I have my first website up, and I’m trying to optimize it now, in both IE & Firefox…but having minor issues…

http://mikepentaproductions.com/

– skip intro, then click any section –

When you rollover the (pentagon-shaped) buttons (in each section), Firefox randomly gets hung up…not loading / unloading the external jpgs fast enough, and then they get stuck and stay visible instead of disappearing “onRollOut”…seems to work fine in IE, just a little slow…

Is there any way I can improve my actionscript to fix this Firefox problem and optimize my images to load faster in both browsers?..(like some kind of “preloader” script or something like that?)

THE CODE:

– (code on the timeline) –

ThmbA.loadMovie(“images/imageA.jpg”);

btn1.onRollOver=function() {
mc1.loadMovie(“images/image1.jpg”);
}
btn1.onRollOut=function() {
mc1.unloadMovie(“images/image1.jpg”);
}

– (code on the buttons) –

on (rollOver) {
setProperty (“ThmbA”, _visible, “0”);
}
on (rollOut) {
setProperty (“ThmbA”, _visible, “1”);
}

any help would be greatly appreciated…thx