If you want a faster way to copy URL of the web page you’re currently seeing than right-clicking on the address bar and select Copy or pressing F6 followed by Ctrl+C, and if you happen to use Tab Mix Plus, you can add a custom shortcut to do the job in just a single click.
This feature is inactive by default. Here is how to enable it.
1. Open your Firefox add-on manager
2. Find Tab Mix Plus from the list of add-ons within the manager and press the Options button
3. Click “Menu” and then the Shortcuts tab.
4. Find the shortcut box for “Copies the tab’s URL to the clipboard”
5. Add your own shortcut in the provided space. You’ll be notified if the shortcut you add has already been used.
6. Hit OK to activate the new shortcut and close the window at once.
From now on, you can just hit the hotkey anytime you want to copy the URL link.