Blocking E-Mail Addresses That Are Not ".com" or ".net"

Hi, I know how to use the e-mail blocking feature in Firefox Spam settings, but find it is limited to blocking only ".com" or ".net" e-mail addresses. I am getting others, including some with many components to the right of the "@" sign, sometimes from foreign countries (an example would be "bargain@aaa.bbb.ccc.ddd.in"). Firefox will not accept such an address for blocking. Is there a way to unlock the Spam e-mail address ".com" or ".net" restriction so that it will accept any address for which blocking is desired? Can this restriction be simply eliminated by Firefox programmers? Thanks. MR