Firefox extensions that use Java are not working with the new Java Plug-In. There appear to be at least a couple of reasons for this:

  - The URL for such extensions starts with "chrome://", which causes a MalformedURLException when parsed by the URL class when producing the document base for the web page. This is causing some of the initialization code for the applet container to bail out.

  - Based on discussions with Mozilla it appears that the JavaScript in browser extensions is granted full privileges, and the previous OJI implementation of the Java Plug-In was informed of that fact when making JavaScript-to-Java calls. Most browser extensions that use Java rely on these elevated privileges. With the new Java Plug-In we do not have the ability to determine on a call-by-call basis whether additional privileges should be granted. However, it seems we need to figure out some way to do this on a page-by-page basis, or in particular, whether we are running in the context of a browser extension.

There have been a few reports of this problem. One is on the forums at http://forums.java.net/jive/thread.jspa?threadID=45933&tstart=0 . Another way to provoke the first failure is to simply load the URL "javascript:alert(window.java);" in Firefox. An extract from an email exchange on this topic with another (large) test case is attached.