You may now add multiple World Clock Times to the toolbar popup!
The "World Clock Time" add-on allows you to create a browser tool bar pop-up that displays world clocks.
Simply choose as many clocks as you wish from the drop-down menu in the pop-up. Please keep in mind that at this time, there are a maximum of 34 options to select from. You can also set the daylight-saving value before adding any item (i.e. -1, 0, and +1). The toolbar popup may be dragged around; all changes will be automatically saved to memory. By default, 9 items are added to the toolbar popup; however, they can be removed at any moment by clicking on the cross sign next to each one (remove button at the top-right corner).