I have lot of account creation tickets, so is one of them going to be used ?

Yes it will automatically use one of your tickets.

And can I do all these in browser extension ? or I need to download the app ?

This feature is only for mobile since it requires scanning a QR Code.

I see the browser extension that I am using does not update on its own ?

If you installed it from Chrome Store or Firefox Add-Ons Store, it should update on its own.