When trying to debug problems like this, a good first step will be validation:
http://validator.w3.org/check?verbose=1&uri=http://www.gherkin.co.nz/tester/
There are some other problems, but the one that seems to be causing the trouble in some browsers are your images' repeated ID attributes (element ids should be unique), and the onmousover/onmouseout ids you're targeting.
In your case, the changer2 function that's called when hovering over elements is looking for images by id (using document.images[id]). Firefox returns a single image, and some other browsers (chrome, presumably safari) returns an array of images, and then the function doesn't work as expected.
So, step one: fix your ids, and the 3rd argument of your changer2 functions.