I'm using the latest version of firefox on win7. Upon further investigation, I think I know what happened now. There's a tiny box at the left of the address bar that enables me to unblock notifications for the site. Which means I must have automatically pressed the "disallow" button before even reading anything (a reflex response!). If I was you, I'd have an option to see a screenshot showing how to unblock notifications. It's always the stupid little things that can make a very big difference.