Firefox, the web browser, doesn't make any decisions about what mail should be considered spam or what senders should be blocked. What email software or webmail site are you using that is rejecting the messages? If it's a common site like Yahoo! mail, Gmail, Windows Live Hotmail/Outlook.com, then perhaps a volunteer familiar with their specific settings can help. If it's Thunderbird, the support site is over here: [https://support.mozillamessaging.com/]. If your security/privacy software filters your mail, you will want to check its settings as well.