The problem seems to arise from misuse of
document.getElementById.
Start the error console in FireFox and press [Clear].
Reload your page and you will see error messages relating to your pages similar this:
TypeError: document.getElementById("icon4") is null
Source File:
http://www.rula.co.uk/rula_scripts.js
Line: 260
Find all the elements referenced, and give them an
ID that matches their current
name attribute.