Posts error

Hi all! This problem started today I think after adding my own apache servers of .php, .php3, .php4. My blog is working fine but when I click posts or add new the page do not opens instead firefox prompts to download this file edit.php and post-new.php please tell me how can I resolve this problem. This only happens with firefox.
I am using firefox 3.6.8 and wordpress 3.1