As many other users mentioned, this stopped working the last time Capital One put out a new version about a month ago.
For me, when I click on the Eno logo and "Checking Session" appears, if I need to sign in a new window pops up for the login but then immediately shrinks and closes with out giving me the opportunity to put in my credentials. I was able to make it work again for 2 uses by uninstalling and reinstalling the add-on. Also, the work arounds others mention, go sign into C.Ones website, then open a new tab (or three) on the same retailer allow me to struggle through.
Honestly, I may drop Capital One if this isn't fixed, there are competitors with apps that work.

EDIT: As promised, updating to the 5 stars this extension deserves. Thanks for fixing the login bug on Firefox, CapOne devs!


So bummed, this extension is/was fantastic, but with newer FIrefox releases it's impossible to use. As dozens of other reviews state, it's no longer possible to sign into the extension. It pops open another browser window for you to authenticate to CapitalOne, but there's no communication between windows so the extension will sit there forever with the 'waiting to sign in' animation. If you close the window it opened, the extension drops back to the 'login required' state. It's a never-ending loop so it's now impossible to use Eno. If they ever fix this I'll adjust right back to 5 stars because I *love* this virtual card feature.

I did try disabling all other extensions thinking perhaps Privacy Badger or uBlock were killing some piece of functionality, but even in a 'clean' environment it won't work correctly. The *only* way you can use Eno at this time is if you open a separate tab and sign into the Capital One site, then you can go back to whatever storefront you had open and Eno will work. Definitely not ideal, you should not have to open a separate tab and sign into Capital One every time you want to use the Eno plugin.