Developing a plugin to be installed automatically

Hi,

We are developing a plugin for printers in windows platform firefox
4.x. This plugin has GUI and needs to be embedded in the web page from
the embedded web server of the printer.

This plugin needs to be installed automatically (user can click find
plugin or install button) without the need of downloading and running
a setup exe, like signed activex in IE.

I found that xpi no longer supports plugins.

Please guide me.

Thanks in advance.

-Shaibu