FF want to download instead of showing the html-site

Hello,

I currently upload the new CKEditor (before I was using the FCKEditor)
So I want to open http://www.example.com/ckeditor/_samples/index.html, but my FF 3 want to download the index.php instead of open the site.
In IE it works corect.

Sometimes I also had this problem on some server with the FCK-Editor.

Someone knows how to fix it?

Matthiasnet