Bravo! (And some ideas) Rated 4 out of 5 stars
First thank you very much. This feature is expected by many people for a long time, I guess!
Some ideas :
+ A bugtracker (github?) to have a place to get involved and submit ideas.
+ Bug: The "titlebar" option doesn't seem to work on my nightly 26 (as it's the only way to make difference between windows)
+ Affect an icon by profile (or a color for beginning).
+ Impact firefox's window icon according to the profile icon/color (as in Chromium)
+ Merge the buttons with the "new private window" in the menu as it's globally the same purpose.
+ Add an entry in the context menu of links to open it in a window of another profile (merged with the "open in link in a new private window" maybe).
+ Add a button to share the "sync" configuration between profiles.
+ Switch to the window of another profile if it's already launched (currently the "Firefox is already running, but is not responding..." dialog is opened).
+ Install Profileswitcher automatically on new profiles created through this excellent extension.
Anyway, one word : OTTIMO, EXCELLENT, GÉNIAL, WUNDERBAR, MERCI!!
Hu! There's more than one word now! :P
PS : With only a few of this features, it will deserve the last star (and a sixth one with all). ;)