From https://dt8kf6553cww8.cloudfront.net/static/javascript/password_strength-vfl6zoIe7.js line 71

Dropbox.js

if (pwd == 'correcthorsebatterystaple' || pwd == 'Tr0ub4dour&3' || pwd == 'Tr0ub4dor&3') { // easteregg
  score = 0;
	word = ['', 'lol']
	if (pwd == 'correcthorsebatterystaple') {
		// TRANSLATORS this text is displayed rarely, whenever a user selects a password that is from this comic:
		// http://imgs.xkcd.com/comics/password_strength.png
		bubble_text.update(_("Whoa there, don't take advice from a webcomic too literally ;)"))
	} else {
		// TRANSLATORS this text is displayed rarely, whenever a user selects a password that is from this comic:
		// http://imgs.xkcd.com/comics/password_strength.png
		bubble_text.update(_("Guess again"))
	}
}