According Set your shortcuts in Firefox.

If you are using FireFox browser then You can set your keyboard shortcut. keyBoard shortcut the way your FireFox browser to set a "Customizable Shortcuts" name must install add-ons by downloading.

After Install you click the Option in Customizable Shortcuts. After clicking Option, a window will open the click in Shortcut tab, top right corner.

Shortcut Here you will meet the previously set if you want to change them let's set so double click and your convenience.