Apparently a Mozilla plugin is already available in OOo 2.0. The problem with it is that you enable the plugin from inside OOo, which requires that OOo is already installed in your machine.
From the Mozilla OOo plugin specification,
The plug-in works only if a working OpenOffice.org installation is found on the system""
This reduces the usability of the plugin, I think. Developing a light-weight OOo plugin for Mozilla/Firefox which can be installed on the fly could be pretty useful.