The reason why the X's are showing is because it is trying to load pictures that don't exist but are being called in your code for the modules. Whenever a picture doesn't exist at a specified url but is being called in the code an X is put in it's place. The reason why Firefox doesn't show it is because that browser simply doesn't put the X image there, it just simply shows nothing.
Here's an example. Above your image that says Welcome to our new site! It is trying to load the following image at the following url:
http://permaculture.com.au/web/www/web/images/banners/PDC.Minibanner.jpgThe picture doesn't exist at that image so browsers like Safari and IE show the X while Firefox just doesn't show anything. You'll need to edit that module and remove that image. To find what image it's trying to load just right-click on the X's and go to properties; and it will show you the url of the image trying to be loaded.
Hope that helps!