In Firefox Address Bar you can use the keyboard shortcuts undo(Ctrl + Z) and redo(Ctrl + Y) to navigate back and forth of recently closed web pages. These keyboard shortcuts are very useful when you want to revisit the URLs of recently closed webpage without actually opening them.
This is a light weight alternative to Undo Closed Tab(shortcut: Ctrl + Shift + T) of Firefox which loads the web pages that were closed recently.
I love finding shortcuts like this. Even though a small percentage of people are going to use the shortcuts, it’s great that developers thought about these useful features and implemented them in the application.
Related: 8 Things To Do With Mouse Scroll Wheel In Firefox