Note: Please don\'t answer with just use Adobe AIR\". I am aware of it, and it\'s not applicable in this situation.
I\'ve been reviewing the Gecko Plugin AP
Yep, check out ScreenweaverHX:
http://haxe.org/com/libs/swhx
http://code.google.com/p/screenweaver-hx/
HTH
nspluginwrapper implements browser-side npapi to make a proxy allowing 32-bit plugins to be used in 64-bit browser, and has fewer lines of code than a browser, could be a good starting point if you want to implement it.
also maybe unrelated but aiming at similar environment is chromeless, a derivative of Firefox which is a lightweight browser which doesn't have an interface, useful to make a desktop app out of html, javascript and plugins.