Firefox vs. IE: ymouse reported differently

Hi,
I’m having some problems with a flash movie. I have a large grid of
photos (as movie clips) that are put on the stage dynamically. I’m
trying to detect when the mouse is over one. The stage dimensions once
the photos are added are 476 x 3752.

In Firefox 1.5 with Flash 8 Plugin, the _ymouse position reported is
way off as soon as you scroll to a location where you can’t see the top
or bottom of the stage. It reports as if it’s near the very bottom of
the stage even tho it is much closer to the top.

It works fine in IE.

Does anyone know of any reported differences in behaviour between
browser plugins, and more importantly, a way around this problem? It
messes up all my program logic.

function applyMouseOver(mcClip) {
trace("_root.xMouse=" + _root._xmouse + " _root.yMouse=" +
_root._ymouse);

}

Here’s a sample of what shows up in IE as i roll the mouse over each
photo going down the page:
2005-12-08 16:55:22 _root.xMouse=59 _root.yMouse=197
2005-12-08 16:55:22 _root.xMouse=57 _root.yMouse=282
2005-12-08 16:55:23 _root.xMouse=47 _root.yMouse=365
2005-12-08 16:55:27 _root.xMouse=24 _root.yMouse=473.95
<!— This is where I have to scroll the browser down slightly to see
the next movie clip —>
2005-12-08 16:55:30 _root.xMouse=53 _root.yMouse=533.95
2005-12-08 16:55:33 _root.xMouse=44 _root.yMouse=616.95
Here’s what shows up in Firefox:
2005-12-08 16:57:23 _root.xMouse=25 _root.yMouse=57
2005-12-08 16:57:25 _root.xMouse=63 _root.yMouse=116
2005-12-08 16:57:26 _root.xMouse=24 _root.yMouse=226
2005-12-08 16:57:26 _root.xMouse=21 _root.yMouse=296
<!— This is where I have to scroll the browser down slightly to see
the next movie clip —>
2005-12-08 16:57:29 _root.xMouse=21 _root.yMouse=3518.8
2005-12-08 16:57:31 _root.xMouse=52 _root.yMouse=3556.8
2005-12-08 16:57:32 _root.xMouse=51 _root.yMouse=3640.8

Thanks for any insight you may have.

Paul