Firefox is a web browser and doesn't do "POP", whereas an email client like Thunderbird would need to connect to a POP-server. --------------------- You posted in the Firefox support fora queue. Firefox doesn't do email, it's strictly a web browser. If you are using Firefox to access your mail, you are using "web-mail" such as Yahoo!Mail or Gmail. You need to seek support from your service provider or a forum for that service. If your problem is with Thunderbird, let us know and we can move this thread to the Thunderbird support queue. https://support.mozilla.org/en-US/kb/problems-with-email-how-to-find-help