a puppet worked by strings: the bird bobs up and down like a marionette.
a person who is easily manipulated or controlled: many officers dismissed him as the mayor’s marionette.
Marionette is the remote protocol that lets out-of-process programs communicate with, instrument, and control Gecko-based browsers.
It provides interfaces for interacting with both the internal JavaScript runtime and UI elements of Gecko-based browsers, such as Firefox and Fennec. It can control both the chrome- and content documents, giving a high level of control and ability to replicate, or emulate, user interaction.
Head on to the documentation to find out more.