BTW, I wrote an Offline QR Code Generator. (on GitHub)
I found many other QR code add-ons too “heavy” or cumbersome and not really user-friendly. Many also use Google Web APIs for generating the qr code, while this add-on works completely offline.
However, it also has some nice unique features like resizing the QR code in an easy way, which AFAIK no other add-ons has. You can also, easily generate a QR code from your own text.
And it even has color support.
While creating it, I tried to make it lightweight, functional and intuitive at the same time. (Not too easy, but actually worked quite well IMHO.) And of course caring for your privacy… 
So feel free to try it out! It still has no reviews on AMO, e.g.