Update 8/20/2019 - The last several times I've tried to use Eno, I get the " 'Something went wrong' What, exactly? Well, that's what my team is busy figuring out. Please try again later." I'm removing the app until it starts working again! Took it from 5 stars down to 1.

Update 5/4/2019 - Apparently Eno is no longer supported by Firefox. "Eno from Capital One could not be verified for use in Firefox and has been disabled."

This is a terrific add-on! Added to Firefox toolbar. Works seamlessly. Click on the Eno icon in the toolbar to create a virtual card, select a virtual card you've already used on a website, or manage your virtual cards. Secure way to shop without compromising your actual card number. BTW, this also works for Chrome equally well.