I have some issues with a PHP file that is not working properly. The Content-type does not get recieved by any browser at all. Firebug interprets the file as text/html inste
the reason is because the header function works only if it is the first one to be called!
If you put an echo before, the content type automatically becomes text/html
try to print a CSS code after the header to test if it actually works.
Read this page for more infos
EDIT: did you change your post ? :-)