Enabling UniversalXPConnect privileges

[Daniele Development-ML]

Hello everybody:
I am producing a small web application that download a jar file containing a
script and two data file. The script needs to access the data file and
activate a plugin that is already installed in my Firefox.

I got this error when doing this:

Error: A script from "jar:
https://localhost:8543/jarRetriever.do?app=example!/chrome/content/example.xul"
was denied UniversalXPConnect privileges.
Source File: jar:
https://localhost:8543/jarRetriever.do?app=example!/chrome/content/example.js
Line: 9

Line 9 of the script is:

netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect")

The plugin works great with other file I can download from the net, also
downloading another signed jar and used in my local server works too. My jar
is signed with a private key I generated with keytool.

I searched in the net, but it seems many posts are mainly on reporting the
problem rather than the solution.

Let me also say that I am absolutely a new by at Firefox - please be
detailed as much as you can, if you can help.

Comments/suggestions highly appreciated.

Thanks!

Dan