I have developed a newer version of my JavaScript event handler code which should run under IE, FireFox and Chrome.
There may be problems under older versions of FireFox, so please test this out and let me know if it works in FireFox, and which version of FireFox you have tested it with.
To test this, please download and extract the files, then run the web page in FireFox and press your arrow keys. The red square should move accordingly.
I have tested it on FF 15, so hopefully it should run well for all later versions at least.
(edit) The attachment has been superceded.