To prevent participants from surfing the internet or using the back and forward button of your browser, it is advisable to run the experiment in a `Kiosk' - i.e. to display only the page, without any menus, title-bar, etc.
I found the following hint at comp.infosystems.kiosks (this link seems to be down at the moment).
user_pref("signed.applets.codebase_principal_support", true);
<html>
<body>
<H1>Please Wait...</H1>
<SCRIPT LANGUAGE=Javascript>
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserWrite");
window.open('exp_menu.html','temp',
'titlebar=no,left=-1,top=-1,width=1024,height=768,alwaysRaised=yes');
</SCRIPT>
</BODY>
</HTML>
...where exp_menu.html is the page that the kiosk shows first.
Notice that now Java Script can do really bad things! Thus, selecting links for the kiosk should be done very carefully.
The following is a quotation from a Netscape tech note
In Netscape's Capabilities-based security model for Java, a principal is a token representing the originator or source of a particular class. By default, Communicator will only allow principals that are based on cryptographic certificates, such as the Object Signing certificate(s) in a signed JAR file or the SSL certificate in an https codebase.
However, it is often quite useful when developing secure Java code to bypass the signing stage in the development cycle. For this reason, developers may place a line in their preferences file to activate codebase principals. With codebase principals activated, Communicator will allow the CODEBASE of the applet, (whether a file: URL or http: URL) to function as a principal for enabling privileges.
Once you have activated codebase principals, be very careful when surfing the Internet. You will always be prompted by Communicator when an unknown applet attempts to enable privileges. Any codebase principal you run across should be considered suspect, as there is no way to verify the identity of its creator or even the integrity of the bits as they travel from the host machine to your own.
Again, this preference is meant for development use only, and should not by activated for most end-users.
In order to activate codebase principals, you will need to edit the file "prefs.js", which is located in your Netscape Users/<username> directory (the exact location of the Users directory varies from platform to platform and machine to machine.) Be sure to edit this file only while all instances of Communicator are shut down, as Communicator will overwrite prefs.js when it exits. Now, add this line to prefs.js:
user_pref("signed.applets.codebase_principal_support", true);
That's it, your Communicator should now be able to support codebase principals.
Last Updated: Tue Jun 24 02:10:03 1997
Copyright © 1997 Netscape Communications Corporation