I too was having problems on Firefox and I will NOT use Chrome. I think I may have found a fix/workaround for all you Firefoxers. It appears the Eno extension does not like multiple tabs open. I close Firefox and when it restarts I just go to the site I'm purchasing something from and Eno works. When I'm done I go to History>Restore Previous session and Firefox will load the 50 tabs I had open from before. I hope this works for you because Eno has become a part of my online process.

As easy as it gets, click on my eno Man and click create... done.

I have used Eno for about 3 years now. After having credit cards stolen in the past and developing paranoia about enter my credit card information online, Eno seemed like a good alternative. So far, it continues to work extremely well for me. 3 websites that I used were compromised and within seconds I was able to shut those virtual numbers down without interrupting my main account. Eno sends me text alerts whenever there is something questionable, and I can react in real time if necessary. I have had some issues with the app after some updates have occurred to my computer, however, I have always been able to get quick resolution to my issues. (Note here, Pre-COVID 19) All in all, I am very happy with Eno.

After dealing with the total pain of having my credit card details stolen recently for a different credit card, I decided to give this a try. I used it for the first time today and it worked flawlessly. I love how the window pops up and then autofills my virtual card number. Very cool!

I installed it 2 months ago (didn't have to disable/remove any of my plugins or extensions or pop-up blockers, I just searched for Eno in Firefox add-ons & installed on Windows 8.1 w/ Firefox 72.x, later Firefox auto updated to 73.x, 74.0 w/ no problems to virtual card# use) - easy install, no need to restart Firefox or laptop. It's worked great for me since then on many online retail sites. When using for the 1st time on a new retail site, it requires 2 factor authentication w/ your cell, after that it'll save & reuse the newly assigned virtual card# for that site (it also auto fills in the payment form). Each site gets it's own different virtual #. You only have to type in your name on the payment form.

to eveyone that cant get it to work. 1) remove any popup blocker. 2) drag and drop virtual cc # onto wherever you are putting the virtual number. 3) i did the later and then rebooted my computer

Seems like a good idea.

Jan 27, 2020: Works great and easy to use.
Have used it on all the websites where I have subscriptions with no issues. Add on will autodetect a page where CC info is to be entered and launch itself to allow you to link / generate a unique CC number for that site. Websites where it has worked flawlessly: Amazon, Netflix, PayPal, NY Times, CuriosityStream, Comcast. On most of the above, the CC info auto-populated into the correct fields, and on the couple of instances where it did not, the handy "Copy" button allows you to copy / paste the info where needed, or you can enter manually if you choose. The settings cog, which leads to Capital One's VirtualCards website itself also works very well to allow you to see / manage your virtual CC numbers.

Highly recommend this addon.

Works Great!!