Hidden tabs after shift-click

Ah, I see now what the difference is that you're referring to. If I understand you correctly, this is actually not specific to Firefox at all--you want to see application windows listed horizontally at the bottom of the screen.

In Oneiric Ocelot, the Ubuntu Classic session type, which has a bottom panel containing a Window List, was removed. However, there are other options for getting a bottom panel with a Window List:

(1) If you still want to have the Unity launcher, and you want everything about your desktop to work the same way except also having a bottom panel, then you can install the package called gnome-panel in the Software Center, then make it start up with your session (click the gear/power icon at the upper-right corner of the screen and click Startup Applications... to bring up the Startup Applications Preferences window, then click Add and add an entry for gnome-panel, where gnome-panel is the text you put into the "command" field). Log out and back in and you should see gnome-panel (as well as the Unity panel you had before, which provides only a single top panel and is less customizable). The gnome-panel will probably not look right to you, so you'll want to customize it, remove parts (or whole panels) that you don't want, and so forth. You can do that by right-clicking on what you want to delete or move or otherwise change, and using the menus. If you do this and need help, please feel free to ask for it.

(2) If you don't still want to have the Unity launcher, and want something maximally similar to Ubuntu Classic (the interface you had before the release upgrade to Oneiric), then you can use a GNOME Fallback session, which in Ubuntu is called GNOME Classic. To get this, install the package called gnome-session-fallback in the Software Center, then log out and log in with a "GNOME Classic" or "GNOME Classic (no effects)" session type. (To select between different available session types, click the gear button on the login screen--this brings up a drop-down menu showing all of them.)

(3) If you don't like GNOME Fallback, then you might try an altogether different desktop environment, such as Xfce (install the package called xubuntu-desktop and select Xubuntu as your session type, even if there is another session type available called Xfce). Besides GNOME Fallback, you'll probably like that best, as it is the most similar to what came before (even though it, too, is different in a number of respects). Other available desktop environments where you get a window list visible all the time at the bottom of the screen include LXDE (install the package called lubuntu-desktop and select Lubuntu as your session type, even if there is another session type called LXDE), and KDE (this is, in a way, the most different, in that there is much less overlap in the components of this DE with others, than between the others, but you might want to try it--if so, install the package called kubuntu-desktop and select Kubuntu as your session type, even if there is another session type called KDE). There is also a standard GNOME 3 desktop (GNOME 3 with the GNOME Shell instead of GNOME 3 with Unity, which you are currently running), but that does not have a window list, so you almost certainly don't want it (but if you want to try it, you can get it by installing the package called gnome-shell and select the GNOME session type).