Longest. Marathon. Ever. FXX To Air First 25 Years Of THE SIMPSONS Over 12 Days!! Read the full article on AICN I am – Hercules!! FXX will transform itself into The Simpsons Channel for 12 days as it runs every episode of history’s longest-running scripted series. That includes “The Simpsons Movie” and the series’ 25th season, which just concluded on Fox May 18. EVERY.