The sale will end at midnight on November 15, and the sale only applies to flights taken between November 26 and February 13, 2019. (Additionally, if you buy before midnight on November 14, some flights are eligible for a 25% discount with the code "SAVE25.")
Of course, this is a low-cost carrier, so buyer beware. The prices are low with airlines like Frontier because there's often a less than exciting on-time arrival rate, and you're going to get charged for bags, food, and seat selection.
But if that doesn't dissuade you, there are cheap tickets to be found here out of a ton of U.S. cities. Treat yourself, because the holidays are coming with all the terrifying fury of winter in Westeros.