The current prototype of the new Java Plug-In for Mac OS X is a Cocoa
plugin for Safari written using Objective-C. While this plugin model
is simple, it has some significant disadvantages. First, the plugin
works only in Safari and not in Firefox 3 on the Mac. Second, the
Java/JavaScript bridge for Objective-C and Cocoa plugins in Safari is
deficient. There is no good solution available for implementing the
new plug-in's Java/JavaScript bridge using a Cocoa plugin.

In the time since the initial prototypes were developed, WebKit has
been upgraded to use the latest versions of the NPAPI and NPRuntime
headers shipped with Firefox 3. This means that the Firefox version of
the new Java Plug-In should be able to be used in Safari on the Mac,
and that this is the least effort solution for both Java and WebKit.