A tab presently gets closed if it is double-clicked and I have, more than a few times, closed tabs accidentaly.
I'd love it if a right-click option to undo the last closed tab was added in a future update.
Or you could add a mini-history list displaying the last 10 or so pages.
Other than this and the absence of drag-and-drop support for URLs from other windows, I think MX Nitro is a wonderful product!