Hi, I have installed all QR code on the Firefox Add-Ons Store, and find this is the only one suitable for me, thanks for the developing for six years.
But I have some suggestion:
1. The icon in the address bar is mainly green, makes it too eye appeal (since other things in address bar is black, white and grey), I am wondering if you can redesign the icon in address bar (maybe directly use an open-source QRCode icon).

2. The text (under the generated QRCode) has white background, it can be good when in a light theme, but when it comes to a dark theme, it does not look harmonize. Maybe the text under the QR Code can show differently depends on Firefox's theme. For example: white text color with black background when dark theme, and black text with white bg when light theme detected.

Now the icon is in page actions, this is good. But the icon is different from the standard style of Firefox. And small scale. Draw, please, a similar icon. The text is also in a different style. "Make QR Code" looks better.
Thank you for this addon.