Mozilla does not support the non-standard document.all object. I believe the ECMA standard says that you should use document.getElementById(id) to get at particular elements and document.getElementsByTagName(name) to get at a list of all the tags of that name.
Boris, you're right, getElementsByTagName() and GetElementsById() is the standard way of doing things (it's defined in the DOM spec however, not in the ECMA standard), document.all is a proprietary IE specific property that is not supported in mozilla. Replacing document.all.tags("...") with document.getElementsByTagName("...") in the testcase makes it work in mozilla. Marking WONTFIX.