Starting Firefox 78, you can able to reopen multiple tabs you’ve closed by selecting the “Undo Close Tabs” option present in the Tab Context menu.
Generally, if you close a tab in a web browser, you can able to reopen it by using the Ctrl+Shift +T shortcut. In Firefox, you can also use the “Undo Close tab” option present in the tab right-click menu.
The ability to open last closed tab with a keyboard shortcut is there in Google Chrome, new Microsoft Edge, Internet Explorer, and other browsers also, but these browsers don’t support opening closed tabs in a session in an easy way like Firefox has planned at the moment.
With a recent change landed in Firefox 78, Firefox shows up an option in the tab menu when you close tabs by selecting any one of the two options available in the new “Close Multiple tabs” submenu.
To experience the feature right now
1. Ensure you’re using Firefox 78 or later, browse some websites
2. Right-click on a tab, hove over Close Multiple Tabs submenu and select “Close other Tabs”
3. Right-click on an active tab to notice the “Undo Close Tabs” option, select it to reopen all closed tabs.
Do note the Undo Close Tabs option appears only when you close tabs using the option(s) present in the “Close Multiple Tabs” submenu.

Warning: If you’ve closed hundreds of tabs, then using this option may make Firefox become unresponsive.
Firefox 78 has been scheduled to release on June 30.
Related articles:
How to Reopen Last Closed Tab in Browsers
Opera removes Instant Search and Tab Menu, introduces Search in Tabs
You can now Close Other tabs in Chrome with a keyboard Shortcut via an Extension
Chrome 78 stable update brings back the “Close other tabs” option to all Users