You can find more information about this question in How to disable the grouping of windows on the launcher?
But in general here is what I wrote (Could not merge the 2 questions because of the bounty). Also note this applies to 12.04+. And is specially noted and useful on 13.04.
The reason why this feature is not available is because of a productive (and actually not counter-productive) reason. Please give me a second to explain so you can also understand. Follow me on this one for the reasons behind this:
Imagine you need to open not 2 Firefox Windows, or 4, but 10 or 20. Now imagine having the Unity Launcher with the common icons it has plus 10 to 20 firefox icons there. You would see 10-20 firefox icons, all the same, and would first have to guess which one takes you to the webpage you wanted to go. Secondly, if you wanted to close them you would have to go, one by one and start closing them manually.
So we have 3 issues:
- If a user wants to open many windows of the same program.
- If a user wishes to switch easily between all opened windows of the same program.
- If a user wants to close many windows of the same program.
With this 3 issues an idea came to mind. Group them together in a single icon in the Launcher that represents the application in use and offer in a one right click solution, all the options needed to cover the rest of the issues.
Between 12.04 and the soon to be release 13.04, there has been much work put out to not only solve this 3 issues, but to help the end user work faster and easily, with just a minor learning curve. The end result (For 13.04 for example) is an icon that can deliver many windows of the same application and offers the possibility to change between them in an almost one click solution.
Not only can I manage several windows of the same app quickly from within one launcher icon, but if the need arises, I can close them all with the "Quit" option in the launcher icon's context menu. Saving me time in case I had 20 Firefox Windows opened.
I also felt the pain when I could not access my multiple windows in an easier manner, but after using this method, I found it was easier, quicker to search in, since I did not have to go through many launcher icons to guess which one is the one I was looking for, neither did I have to scroll down the Unity launcher between 20 Firefox Windows, 30 Chrome ones and 40 Nautilus ones just to get to the one I needed. Overall, it saved me time when I needed to find the correct one and work on it.
As you can see, it focused itself to be more productive to the end user, with just a slight touch in the learning curve.
Now, if you actually wanted to have the option to ungroup them, it would involve, downloading the Unity source and any dependencies related to it. Modifying the code so you could actually ungroup them, by default or as an option, compile this and install it on the system, making your Unity be able to ungroup them as you wish. But in this case, I would ask, is it better than the solution provided by the Unity Development Team?.
This of course is left to each person to decide on how they like to use their system. In my humble and honest opinion, I feel the change made by the Unity team, solves several issues I had on 11.10 or even on 12.04 related to this, and the way it works on 13.04 is much better than I anticipated.
I am sorry there is no straight and specially, easy answer and I really hope you can take a moment and test out the behavior of this feature as it is on the latest Ubuntu version (Specially 13.04 if you have the time). For your case, I would encourage and recommend you take the time to upgrade your system, or even better, download the 13.04 version and test it yourself. It is a huge jump from 11.10 in regards to how Unity and the whole system behaves and helps you accomplish tasks quickly. Hope you see it this way too.