Just had a problem with a website which worked fine in IE, however when viewed in Firefox, some of the <A HREF> links weren’t working!

Turns out it was a problem with the z-axis.   One of the other elements on the page was appearing on top of the links and obscuring them.  By using  “z-index” I was able to re-order the elements, bringing the links to the surface again – and all worked fine again.

Here’s a good description of how to use z-index: