Browser windows won't stay where I position them

Hi,

I have a Mac Mini running Tiger, and mainly use FireFox as my web browser.

Whenever I drag a FireFox window to a different part of the screen and let
go the mouse, if the window is being refreshed at that time it jumps
arbitrarily to another part of the screen, usually its previous position but
sometimes to one of the corners.

This tends to be when viewing streaming media such as concert footage, band
videos etc, but also happens sometimes with MSN or Yahoo Messenger.

Is there a setting somewhere to stop this happening - it's immensely
frustrating!

Any assistance gratefully received.

Mark