Rated 5 out of 5 stars
It's good and useful. There is a bug though. This add-on bypasses 'warn me when closing multiple tabs' option and no matter the option is checked or not in Firefox setting window, Firefox never give any warning when closing multiple tabs.
Hope developer fix this soon.
Nevertheless, a nice add-on. I especially like the icon, fits well with the rest of the icons of Firefox default theme.