Firefox is just a web browser and has no email features. If you are using Firefox to access your email, it will be a web based email system and any email features will be part of the web based email service that you are using. You will need to contact the support for the email service to see if they have an "Out of office" option. If your question is about using 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