"I have connected my Ledger via "attach ledger via webusb". When I open the accounts page and hit "Add Ledger" the small window does not open."

That small window is optional and will not appear in some browsers. If it appears, it looks like this: 

You will manually have to select your Ledger in that window to move on. 

However, some browsers skip that step. In that case, have a look at your accounts list and see if your Ledger appears there. If it does, everything is fine.