firefox --install-global-extension does not work on feisty?

[Randall J. Parr]

On other distributions (eg old Red Hat's) using firefox 2.0.0.11 I can 
install global extensions using

# firefox --install-global-extension some-extension.xpi

This does NOT work on my Ubuntu Feisty install though (firefox 2.0.0.11). 
There are no errors; but nothing seems to happen either.

Does anyone know if this does/should work on Ubuntu?

Thanks
R.Parr, RHCE, Temporal Arts