Can't set UniversalBrowserRead

[Rufnex]

Hello,

i try to use external files with mozilla or firefox. so i would get the
rights for this like that:

try {

netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
} catch (e) {

alert("Permission UniversalBrowserRead denied.");

}

But i still got an error like

Error: uncaught exception: Permission denied to call method
XMLHttpRequest.open

So next try was to write into pref.js

user_pref("signed.applets.codebase_principal_support", true);

But this also bring me this error.

Any ideas what i can do ?

thx
Rufnex