Most of us use the tab feature in Mozilla Firefox and open multiple web sites in Firefox. Sometimes, when we open multiple sites using the tabs we might accidentally close one of the tab. Now what? But do not worry, Firefox has a method to open the closed tabs.
When you accidentally close a tab, you can press the key combination Ctrl + Shift + T to open the last closed tab.
When you do this, the browser immediately re-opens the closed tabs and the last URL you were visiting in that tab. The number of times you press Ctrl + Shift + T, it will re-open previous closed tabs in your browser.
You can also open from menu History → Recently Closed Tabs and choose which closed tab you would like to open as shown in the following picture :
To open all the closed tabs, choose History → Recently Closed Tabs → Restore All Tabs as shown in the above picture. Note, that if you have a lot of closed tabs in the list, be careful when choosing this option to open all of them.