does anyone know how to code a popup window so that it pops up as a new TAB in firefox, rather than in a whole new window?

You won't be able to do that, because what will happen when people in another browser click the link?

You can't do that for everyone but just for you(and anyone who uses your computer/broswer) install a extention like Tab Mix (http://www.extensionsmirror.nl/index.php?showtopic=2291) and put that as a setting.

ok thanks

thats really annoying but thanks for the replies

Your welcome :)