unable to add additonal emails

I just changed computers and I got my one email in and it is checked but I am unable to add an additional anyone have any ideas/suggestions

You should sync your emails to the web browsers such as Chrome / Firefox . I always make sure my emails are sync to the web browsers . I have certain email for Firefox and certain email for Chrome and also all my extensions are added as well . You could try deleting history, deleting cache, deleting web browser history and try adding the new emails. Also refresh XN 42.13 and refresh your browser. 

How are you unable? 
You can't add custom scripts to X-Notifier 4.x for Firefox... changes in the browser negated custom scripting.
Otherwise... what email are you trying to add?  What happens?