The new tab extension works exactly how I like. Except I would love it if there was an option that stops the last tab from closing unless you click the close button.

* Edit
Right now ctrl W will close the current tab, if you have lots of tabs open and you hit ctrl w several times it will close them all and eventually close the browser window. It would be nice to check a box to turn this option on or off.

To prevent this from happening right now you have to go into the Firefox preferences: about:config and set the browser.tabs.closeWindowWithLastTab pref to false.

BTW, being able to focus on window and usability are the main reasons this add-on is superior to all the other "new tab" type add-ons out there right now. Great Job!