I was developing a web page. This web page submitted data in an html form to a php script. The php script returned data for downloading by the client using the following header tag:

header('Content-Disposition: attachment; filename="'.$file['name'].'"');

Unfortunately all my downloads got blocked in my Firefox 3 browser. The message was:

This download has been blocked by your Security Zone Policy - mywebsite.com

Or in dutch:

Deze download is geblokkerd door uw beleid voor beveiligingszones - mywebsite.nl

According to the Mozilla help pages this problem has many solutions on the browser side, such as re-installing Internet Explorer. Fortunately I did not spend much time on them.

I found out that if I were sending less data to the server then my browser did not block the download. So the problem was related to sending too much data in the GET request to the server.

After I added "method='post'" to the form on the html page my browser let the downloads through, they were not blocked anymore.

So the problem was in the HTML page and not in the browser.