IE applies transformation, Fx does not

Hi list,
I've a xml file with a transformation specified:
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="../view_names.xsl" type="text/xsl"?>
<doc xmlns="http://www.w3.org/1999/xhtml">
...
</doc>
When I call a file like this, either from the browsers address bar or via
a normal link, the file is fetched, gets transformed and the result
is displayed, for both Fx 1.5 and IE 6.0.
When I fetch the file via javascript httprequest, then IE applies the
transformation before giving me access to the result-tree, but Fx gives
me the input-tree. Now my questions:
1. Is there any standard for this case or is it simply implementation
defined?
2. May I influence one or the other, anything like a switch to
force or prevent the transformation?
3. What may I expect from Safari 1.3+ in this case?

Regards, Manfred