The dataFile parameter was just appended to the applet's codebase url. This cause errors when the applet's codebase url (the webpage url in firefox) was a parameterised url. EG: http://localhost/treemap?option=2 , with a dataFile = 'data.xml' the url lookedup was http://localhost/treemap?option=2data.xml !
I patched the applet to use the codebase url as the Context instead which not only fixes this issue but gives you more flexability for the dataFile url.
Patch to use codebaseUrl as a Context for dataFile
fixed in 1.1.1