Emacs Dvorak Keybinding wót Huy Tran

This is a fork of this addon https://addons.mozilla.org/en-US/firefox/addon/emacs-keybinding/ but modified to be used efficiently with Dvorak keyboards.

The changes is:
- C-f and M-f now become C-h and M-h
- C-w to close tab
- C-f to focus on first input
- C-x n to create a new tab