The http://www.emacswiki.org/emacs/ELPA, standard with Emacs 24+, includes the Factor major mode called https://www.google.com/#q=fuel+factor+mode+emacs.

Setup Emacs

1. Install the Fuel package

[M-x package-list]

Find the Fuel package, mark it, and install.

2. Set the Factor root directory in .emacs

[(setq fuel-factor-root-dir "/Applications/factor")]

Run Factor Listener from within Emacs

[M-x run-factor]