You have an on the fly rendering engine to view an IE7 display, in the status bar, it has additional options, to open in new tab. I forgot that I had added this add-on. It is not part of t Firefox 3.0 RC2. It is a useful tool when you cannot view a page with firefox or for web developers not wanting to change between browsers, switch on the fly to a IE tab. This works with Firefox 2 and the current Firefox 3 RC2 release.
https://addons.mozilla.org/en-US/firefox/addon/1419