Hi and thanks a lot for your rating. I'm sorry that the extension is not working as expected for you. As far as I understand, you cannot see the extension icon and you want to download the QR code.

So as for the first issue, you are right, your browser should have a colorful icon. See the video here for an example on how to use it: https://github.com/rugk/offline-qr-code/blob/master/assets/screencasts/qrText.gif
If you cannot see it, it may be shown in the extension menu, where you can also pin it to the toolbar menu. See https://support.mozilla.org/kb/extensions-button for more explanation.
Apart from that, you are correct Ctrl+Shift+F10 is the default (though configurable) hotkey, as described in the add-on description and Readme on GitHub.
Note you can also open the QR code via various other ways as a context-menu e.g. when right-clicking on links.

As for the second issue, here is how you can save the image as SVG or PNG: https://github.com/rugk/offline-qr-code/wiki/FAQ#how-to-save-the-qr-code-on-disk

The thing is Firefox recently changed how such a menu icon would be shown by an extension and introduced the extension menu/button. There is no way for the extension to change this, you need to manually adjust, which extensions you want to show there. Note this applies to all extensions, however.

It would be glad if you could upgrade your voting to 5 stars if that solves your problem.

If you have further issues or questions, please feel free to get in touch by opening an issue on https://github.com/rugk/offline-qr-code/issues. Thanks.

Best regards,
rugk