Universal Browser Read
If you need to open a popup window that writes back to the parent window, to prevent phishing scams etc, browsers do not allow it by default. In IE it will come up with a permission denied error unless the windows have the same host. However, in firefox, it will deny access even with the same host if the port is different. I had this issues where one app wanted to access another for an intranet application (A domino web app needed to access a tomcat jsp one).
Basically you have to allow the browser the "UniversalBrowserRead" access level.
However, this is automatically denied unless in your browser you have "signed.applets.codebase_principal_support" set to true in which case it lowers the overall security to the same as IE and prompts you that the content could be unsafe and asks if you want to continue.
You can do this in the about:config page in firefox, or by appending the line :
user_pref("signed.applets.codebase_principal_support", true);
In the prefs.js file in the firefox folder.
Once this is set, you then need to use the line :
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
in your javascript code. If you use this within a function rather than on the whole page, then the privilege is reset on the function exiting.