Recently, Firefox has started supporting CoreGraphics and Cocoa Events (or, possibly, it will start supporting this in the near future).
This means they're finally moving away from the MacOS9-era QuickDraw interfaces.
This, in turn, means that an Ambulant plugin for Firefox (and other NPAPI/NPRuntime-based browser) has become a possibility again, because we have some CoreGraphics support (originally done for the iPhone port).
Time permitting, someone should take a look at the following two pages and decide on a course of action:
https://wiki.mozilla.org/Mac:NPAPI_Drawing_Models
https://wiki.mozilla.org/Mac:NPAPI_Event_Models
Came across this thread (well, one message only) that has some interesting insights:
http://groups.google.com/group/mozilla.dev.tech.plugins/browse_thread/thread/99b12d098d927c2b
The NPAPI plugin was completely rewritten 3 years ago (rev.7358) and works
with all browsers (Safari, Firefox, Chrome, Opera and OmniWeb as long as they support plugins).