Could you elaborate if this is with support.mozilla.org, Firefox Accounts or something else?

If you try to connect with your persona account on a firefox os device, the problem is known and there is an open bug to correct that. But it has not been resolved yet

What is wrong with your website?

I spent a lot of time trying to sign in today. I kept being told I was getting a confirmation email, which I never got. I was getting emails from everybody but you. I searched high and low in your site to get help, and there was nothing, no way to get around this impasse, until I finally found page that had the dark orange line going across the top, that asked me to sign in. This time, I created a User ID, which was not required when I originally sign up for Mozilla years ago. I finally got a confirmation email, and was able to sign in. There is something wrong with your website, that it kept telling me an email had been sent to me, when it had not! I was using my email address at acceptable as a User ID