Maybe the current window's user profile could be displayed in the Help-->About Firefox dialog box. (I sometimes have multiple profiles open and would like an easy way to know which profile the current window belongs to.)
We're working on a new profiles feature that is now available to try out in the current version of Firefox Nightly — the feature is turned on by default. If you want to see a video demo and interact directly with the team working on profiles, check out this post on Connect: