August 2019
Always try using chrome guest if anything goes wrong. Flash not launching, video window not working, logging in not working, etc.
Sometimes its your side is the problem because of the website requirements. I'm facing same issue and I don't know why, but tried using guest window and worked flawlessly.
Click on your account picture on top right, then go to the bottom and click on open guest window.
August 2019
Can confirm that I'm unable to log in using Firefox while Chrome works just fine.
It's been an issue for over three years now.
I've no idea why EA web programmers hate Firefox.
June 2020
Thank you so much. This works! And your instructions were super easy to follow.