apache2 and php - firefox wants to download phtml file?

[Micha Feigin <michf@post.tau.ac.il>]

I installed some php application of a server here which I installed
with apache2 (prefork).

When accessing the directory without the trailing index.php I get a
message from mozilla firefox prompting me to save a .phtml file. If I
access it with .../index.php it works fine.

I added .phtml to the php conf files. For some reason it works on one
copy of the program (mostly unmodified) and fails on another.

Its a conference paper submission system. The modified version hasn't
modified index.php and in the other pages only modified page content
and style sheet but not the code itself.

Any ideas?