Hi there, you should be able to see NordPass add-on in the Extensions section in your Firefox browser (look for a puzzle icon on the top right corner).In case you don't see it then go to Manage Your Extensions settings and make sure that Nordpass extension is enabled. When it's enabled you should see it every time you press that puzzle icon on the top right corner.
I hope this helps, otherwise please reach out to us at support@nordpass.com and we will be more than happy to help you.