IE will be rocking it supports for all close options like top.close(),window.close()....

But to close a window in Mozilla firefox you should consider two points...

1.Window should be opened by Javascript
2.If it is opened by JS you can close it thru window.close, like if
window.open('',_self,'');window.close();

Remember here window.open('',_parent,''); works for only some browsers.

Eventhoug you dint open the window with JS but still wanted to close then you have to set
"dom.allow_scripts_to_close_windows" to true in the firefox.For this option goto firefox address bar type "about:config" search for "dom.allow_scripts_to_close_windows" option double click on it to change to true as it is default false.