TO THE DEVELOPER (SUGGESTED NEW FEATURES):
1) --You must allow the user of your addon to just left-click the mouse button once on your icon to have the most recent site opened. As 99% of the time, when I use this addon, I want to simply open quickly the last tab that I closed.
--And use double-click of the left mouse button on this addon icon to open the list of opened tabs to choose to open.
2) Make the icon that shows on the top of Firefox in white to be able to see it better than the grayish color that it has at the moment and that completely disappear on the dark blue that I have for the top of my browser.

I put 5 stars as soon as you implement this vital feature 1.

Thanks for sharing this addon.