Some people expressed the need to work with different languages in different tabs. This was not possible, because the language was stored in session and if you tried this, you'd get some weird behavior.
Just back from the Firefox Summit, I spent some time to change this, so now you can select which language you are translating in at anytime and you can work on different languages in different tabs.
The one thing that's still stored in session is the user data, so you can't be logged in with two users at once in the same browser.
Another thing added is that now you can choose Narro's language independent of the language you are translating in.
There are lots of things that will be added, and a 0.9.2 release will be out soon.