This is the source tree for HTTPS Everywhere for Firefox and Chrome.

Important directories you might want to know about

src/                      The Firefox source

chromium/                 The Chromium/Chrome source 
                          (not to be confused with Firefox browser "chrome" or UI)
 
src/components            |
src/chrome/content        | Firefox JavaScript and XUL code
src/chrome/content/code   |

src/chrome/content/rules  The rulesets live here