Excellente! Most people here are praising MAC for its features, and they're right.
There is one review below by squarrell who finds he has trouble with the extension, but there IS a solution.
I've found that looking for the particular MAC tab for a particular account is irritating. The popup as you hover across the tabs is slow, and you have to run across them until you find the one you want. Better is to use MACs with the Simple Tab Groups extension. STG names them in its vertical dropdown, easy to inspect, and MAC puts an annunciator in the address field. An unintended method, but it works.
All hail Extensions!