Nice and useful feature, lightweight, efficient. Thank you for sharing your work.
One little problem, at least on my Firefox, is that it blocks the Salesforce "login as a user"

Nice overview in the menu, however a quick Login Button is missing as was already mentioned.
Cloud coloring only works in Salesforce Classic at the moment.

Overall nice add-on. It has a very pretty user interface and it's smooth. For me, it's just missing a quick shortcut to log in, in order to not have to click three times. Apart from that, A+ :)