when i double click a link in mirc while using mozilla firefox 3 it comes up in a new tab though when i do the same thing but with internet explorer 7 it comes up in a new window. is this because of mirc or internet explorer?

This is due to the way Internet Explorer is configured to open url addresses. I understand that IE can be configured to open the addresses in a new tab, rather than a new window, but I've had no luck in actually getting the change made.

You might also refer to this thread, and see if changing the internet-options setting will help you.

https://forums.mirc.com/ubbthreads.php?ubb=showflat&Number=200496