[BNM] Can anybody help with a Xhtml/javascript error in Firefox?

[AndrewGill73@gmail.com]

BNM'ers,

Help!! Calling all xhtml/javascript people....

We've written a simple html page and javascript that switches images -
it worked and everything was fine!

However, then we placed the code in a CMS. This meant the html page
was now XHTML 1.0 Transitional... and it's stopped working in Firefox
(although works in IE). We're scratching our heads how to fix this...

Firefox error console is telling me that the image objects are not
defined but they are !! It appears that Firefox is now rendering in
standard compliance mode (previously it was rendering in quirks mode).

We need the page to be XHTML 1.0 Transitional - how can we fix the
xhtml or perhaps the script so that it works in Firefox?

Here is an example:
http://ns296.pair.com/andygill/test/test1.html (this page is html and
works fine)
http://ns296.pair.com/andygill/zLP1/test2.html (this page is xhtml and
doesn't work in Firefox)
http://ns296.pair.com/andygill/zLP1/swap_images.js (this is the javascript)

Any help is hugely appreciated!

Cheers,
Andy