You are not understanding my point and it looks like you are not paying attention to what the OP is saying.
It takes under a second for the sample images to be scanned on my machine. It's fast. It's pure client side HTML/JavaScript.
If you look on the same page that I linked to then you will see that it can also process video in JavaScript doing the same checks.
Further more, barcode scanning algorithms are plentiful and are not nearly as complex as other processing we are already doing in JavaScript. This demo's algorithm is doing harder work than a barcode algorithm would be doing and performance is very good.
The bottom line is that a barcode scanner application is technically and practically possible. This demonstrates that very well. The Mozilla app store will have no problem creating a shopping app using their web capabilities.