Problems with localhost

Hi,

I’ve decided to work locally on my site, so I installed MAMP and followed all the steps to get it going. I download my wordpress files from cPanel, and put them into applications>MAMP>htdocs.

MAMP is running fine, but when I try to visit http://localhost:8888/mysite, Firefox displays this window:

You have chosen to open:
which is: application/x-httpd-php (418 bytes)
from: http://localhost:8888/
What should Firefox do with this file?
‘Open with’ or ‘Save file’

Any idea why this is happening? The next step would be the five minute Word­Press install- but I keep getting this problem.

Thanks.