Hi, as Firefox is not a Email Client please see how to do that in the Help Of the online website your using or in the program you are using. Firefox has nothing to do with mail other than you may view it. If your looking for Thunderbird Support it is over here : https://support.mozilla.org/products/thunderbird

Some e-mail providers have the option to sort incoming mail. Contact your e-mail provider for help.

Go here and register for protection for your e-mail and phones; https://www.donotcall.gov/ The National Do Not Call Registry