I have tried to set up filters for many junk emails I receive but the filters don't work. Please explain how to set up filters correctly.

Firefox is just a web browser and has no built-in email features. If accessing email through Firefox any email features will be part of the web based email service. You will need to contact the support for the email service for help in using its features. If the question is about Thunderbird, for Thunderbird support you can ask in one of these forums: * http://forums.mozillazine.org/viewforum.php?f=39 * http://getsatisfaction.com/mozilla_messaging