This works exactly as I'd expect. I set my Firefox to open a new tab when you close the last tab. I didn't like the ugly white screen, this allowed me to match the theme at the top. And it was great!
... until I went to scroll on a webpage using my touch screen. It was broken. I'm on Linux, see, and touch screen capability is dependent on e10 compatibility. Which this addon is not. So I had to disable it. So I'm sad. If you don't know what e10 is, then it likely doesn't matter to you, and this is a good addon. Only (other) improvement I wish it had was the ability to address how the background image handles scrolling.