Conkeror is a browser that uses XULRunner and is a highly configurable and programmable browser.
Here is the description of the browser from the homepage:
Conkeror is a keyboard-oriented, highly-customizable, highly-extensible web browser based on Mozilla XULRunner, written mainly in JavaScript, and inspired by exceptional software such as Emacs and vi. Conkeror features a sophisticated keyboard system, allowing users to run commands and interact with content in powerful and novel ways.
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