virtualbox.org

When I download the extensions package it comes downs as a gz file. When I extract I'm not getting an extension of vbox. Unable to install. How do you get the extensions package?

I think your browser is 'helpfully' changing the file extension of the EP to what it really is, a gzip archive, rather than just downloading the file and letting it be. I remember a report if this some years ago. Try a different browser.

Or change the extension of the downloaded file to :

.vbox-extpack

And try it then. If you get the extension changed properly, the icon should change to a green cube.