Firefox Addon 2 - [ LIST ]

Firefox User JavaScript / UserScript

Greasemonkey
Customize the way a web page displays or behaves, by using small bits of JavaScript.

Scriptish
The greatest user script engine on the Internet (a fork of Greasemonkey).

Lubemonkey
(A Graesemonkey fork) Next Generation script manager for Firefox with SQlite Database storage.

Scriptify
Create and manage add-ons made from Greasemonkey and Scriptish user scripts

alternative to:  Tampermonkey