NumExt allows you to add numbers to your opened Firefox tabs for easy organization and access. You now have the option to also add colors to tabs.
Since the number of tabs accessible through Ctrl + number is limited from 1 to 8. With NumExt, you can use shortcut keys Alt + numbers from 1 to 9 for tabs numbered 9 to 17 (KEEP IN MIND, THE ALT key bind only applies to Windows Operating Systems)
Alt + X - enables a small box under which NumExt commands can be entered - The shortcut is customizable.
To close the little NumExt text box, press again on "Alt X"
(NumExt is NO LONGER MAINTAINED since April 2010)