How can I disable the file:// protocol in Firefox?

"I found a way to do this.

First the scenario of our problem is:

We want client to use a PCs and they have access to firefox only
No ""my computer"",""cmd"",...etc.
We want them not to browse local files by Firefox , just browsing some sites.
We want to block file:// protocol that cause browsing of local files.

My suggested solution:

Download r-kiosk extension and modify it to run on firefox 3.5.*
Modify userPref.js to show the address bar in firefox
---- here we stop Save as,open file,remove extension,no viewsource,but users still browse the localfiles by typing file:///c:/ in url.
Modify dirListing.css in Firefox/chrome/classic.jar/skin/classic/(skin name)/dirListing

body{
...
background-image:url(chrome://global/skin/dirListing/forbidden.png)
}
table{
...
display:none;
}

Hide elements like P,H1 by using visiblity:hidden

You can use this image created by me to make it as body background:

Here is the result:"