So you've cloned Scriptish's repository, made your awesome changes, and want to test your changes without building an .xpi from source? Then you will want to make an extension proxy file.
You should read this link for complete instructions, but the basic steps are:
nglayout.debug.disable_xul_cache = true. Disables the XUL cache so that changes to windows and dialogs do not require a restart.
dom.report_all_js_exceptions = true.
devtools.errorconsole.enabled = true.
-purgecachescommand-line flag disables this behavior.
-no-remote. Enables running multiple instances of the application with different profiles (used with
-P. Starts with a given profile name (profile name is case sensitive). If no profile name is provided then the profile manager is opened.