The website in question is http://www.meridiandelta.com.
You will notice on the left hand side is a menu, made up of transparent GIFs. I've put the following Javascript instruction in to turn the background yellow when the mouse is over it -
Example link
<a href="products.htm" onMouseover="this.style.backgroundColor='yellow'" onMouseout="this.style.backgroundColor='white'">
In IE, it works fine, and the whole of the cell containing the link gets coloured yellow. See this -

IE Mouse Off

IE Mouse Over
However, in Firefox and Opera, it looks slightly strange...

Non-IE Mouse Over
How do I get rid of this problem?
TIA.