Excellent! Here's a suggestion. Rated 4 out of 5 stars

Simple and easy to maneuver! I like the way the times of locations are shown at the bottom of the browser. It makes monitoring the time a lot easier. And I get to set the cities I want!

Suggestion: try to allow user to change the color of the font. Currently the font color is black, it makes it kind of difficult for user to see the clock when the brower's theme is also black. I had to give up few nice themes to accommodate with the clock.

This review is for a previous version of the add-on (2.2.23).