I believe the new browser does not support XUL for performance reasons. Among other things, this makes it impossible for extensions to modify the browser UI. This may make it impossible for things like plugin settings windows. Assuming the plugin doesn't require any user interaction after initial setup to do its thing, you might be about to edit any extension setup variable in a text editor.

As an aside, the plugin that I would kill for (but which I doubt would work) is flashblock. Currently, a lot of flash crashes the browser, using the new flash 9 plugin. Browsing the web with flash turned on atm is like playing russian rouletete. There needs to be some facility for selectively whitelist sites.