I just upgraded to Ubuntu 12.04 and have also installed GNOME Do as a task launcher. If I already have a Firefox browser window open, and I use my hot key to open Gnome-do and type in Firefox + enter, it opens a whole new window instead of focusing on the window I already have open.
I'm used to Mac OS X's Quicksilver where it focuses you back to the opened application if it exists already. Is that possible to replicate using GNOME Do or Ubuntu Dash?
This may be different for a mac keyboard, but on a windows keyboard the key combination is win+numkey, with num being the order of your application in the launcher.
You can hold down the win key and get an overlay of applications, and the corresponding number to open them.
Hope that helps!