Here comes an awesome Firefox plugin which lets you display clock of different cities around the world in your status bar ( this is configurable ). So if you hate double clicking the clock and then look around for time zones, this is an excellent utility.
By default it shows around 3 to 4 clock in the status bar but you can always add more countries, cities and timezones. When you mouse hover the Fox Clock, it displays the time of all the cities you had selected in the tool tip. So make sure you prioritize the clocks so the one which you need most is always displayed on the status bar. Add Fox Clock