Undo Close Tab allows you to restore the most recently closed tab with a single button click and gives you access to the list of recently closed tabs in a context menu. Top 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.

Please note:

• There is a known bug in Firefox which may cause Undo Close Tab to not work at all. To revive the addon, you have to reset your browser session
• If there are more than 6 items in the "last closed tab history", then a submenu "More items" is created. This is to workaround a technical limitation of the WebExtension API.
• The default setting in Firefox is to only store information for a maximum of 10 closed tabs. If you want to reach the maximum of 25 tabs, which again is a limitation of the WebExtensions API, then you have to increase the value of the browser.sessionstore.max_tabs_undo preference via about:config.

For an overview of changes, here is the extension commit history.