It is very easy to fake the email address that appears in the From field of an email message. Spammers frequently send emails that appear to originate from your own email address. They do this in the hopes that it may trick your spam filter into accepting the email message. And it works. If your own email address is in your address book or in the Spamfire Senders List, Spamfire will accept the message, no matter how spammy it looks otherwise.
There are several ways you can deal with this problem.
You can simply remove your email address from the Spamfire Senders List and, if you use Mac OS X, the OS X Address Book. Then Spamfire should quickly learn to reject spam messages even if they come from your own email address. Spamfire will also learn to recognize legitimate email messages that you may send to yourself from time to time.
If you never send email to yourself, then your email address in the From field is actually a good spam indicator. You may wish to take advantage of this by adding your email address to the Senders List as a known spammer.
If don't want to remove your email address from the Address Book, and you do sometimes email things to yourself, you can create a Rule Filter that will be more intelligent about what it accepts and rejects. Rule Filters override Sender Filters and since they can check multiple criteria, they are more powerful and flexible. The Rule you create depends on many factors, but basically, you want to create a Rule filter that checks for your email address in the From field and one other criterion that the spammers cannot spoof. For example, if you always include a "signature" at the bottom of your outgoing emails, you could check for your email address in the From field and some of the text of your email signature in the Body. You can create two filters: one that accepts email if that text is found in the body and one that rejects email if that text is not found in the body.