Simply hover over the square target icon on the status bar to generate a barcode of the current page. Right click on a link to generate a barcode for that link and the same goes for text selections.
Download the Tool Here.
Once you download the "add on" you will need to add the tool to your toolbar. To do this, when Firefox is open, choose View on the top menu:
Next, choose Toolbars from the drop down menu, and then, choose customize from the new drop down menu:
You will then need to find the new button and drag the tool button for the mobile barcode to the toolbar from the choices:
Once you have done that it appears on the toolbar like this:
Anytime you are in a website and wish to create a QR code with the current URL:
simply click the button on the toolbar:
and the QR code will be generated, and you can save it as a picture file to share or print: