Firstly I don't think you have tabbed browsing working fine. In FireFox if tabbed browsing is working there should only be one box in the taskbar (The bar at the bottom of your screen). To see what I mean, open FireFox, then right click on a link, instead of left click and choose open in new tab, you should now have two tabs inside FireFox showing different web pages.
You can change your preferences for tabbed browsing under Tools / Options menu, then in advanced settings, there's a section on tabbed browsing.
Secondly. What you are describing is what windows now does by default, and that is to group similar taskbar buttons. To change this, if you right click the green start button, then choose properties. Then select the taskbar tab, and uncheck the "Group similar taskbar buttons" box.