Useful prefs
From MozillaZine Knowledge Base
Add these prefs to user.js (in your Profile):
// Disable XUL cache (so you don't have to restart everytime you change a XUL file) user_pref("nglayout.debug.disable_xul_cache", true);
// Enable dump() (read more) user_pref("browser.dom.window.dump.enabled", true);
// Show chrome errors in the JS console user_pref("javascript.options.showInConsole", true);
// Enable strict JS warnings user_pref("javascript.options.strict", true);