This Add-on seems to be a port from this Opera extension: https://addons.opera.com/de/extensions/details/install-chrome-extensions/

In its native version, it was supposed to support chrome extensions in earlier opera Versions, before they were supported natively.

I suppose this is its ported counterpart for Firefox browsers.
Unfortunately, it doesn't work anymore and therefore is leaving one hole more in our users' extension-toolbox. :'(