Undo Close Tab is a Firefox add-on that allows you to restore (up to 25) closed tabs.
Undo Close Tab is capable of restoring the recently closed tab with a single clickâ€”plus, it can offer a list of recently closed tabs within a convenient context menu.
The author notes that there is a known bug in Firefox that may cause Undo Close Tab not to work. To revive the addon, you have to reset your browser session. During testing, we did not encounter this issue.
Undo Close Tab Features:
Restore your most recently closed tab with a single click of a toolbar button
Quick access to up to 25 recently closed tabs in the context menu (right-click on toolbar button)
Optional access to the recently closed tab list in the page or tab context menu
Integrates nicely with Firefox preset icons and also adapts to nearly every Firefox theme.