It sounded like a great idea...I installed it, it logged me out of Facebook and cleared the FB cookies ast stated, so it got one star. Since installing it blocked all attempts to log in to Facebook. At the FB login page I entered email and password, clicked on the 'Log in' button, but nothing happened, no screen refresh no error message.
When I disabled the add-on, I was once again able to log-in to Facebook.
It did not change the tab colour to blue, I do not have any Multi-Account Container add-ons.
Hence no more stars can be awarded.