ReloadEvery - This Firefox add-on will help you refresh web pages on a schedule. From every 5 seconds and can go on up to every 15 minutes or you can customize your own time. You can also enable it to every tab or single tab.
This is very useful for sites like twitter, news sites and other pages which display frequently changing information. Works with Firefox 1.5 - 3.6.* and check it out here.