It actually had an episode that dealt with time travel.

When they were up in space to watch the supernova, Fry microwaved Jiffy Pop popcorn. The microwave rays collided with the nova rays and sent them back in time. They crashed in Roswell, New Mexico in the year 1947. The UFO that crashed in Roswell happened to be their spaceship. Bender was in pieces and Zoidberg ended up at a government research facility. The Professor and Leela went out to look for a microwave, while Fry and Bender's head found Fry's grandfather, who was stationed in Roswell at the time. When the Professor and Leela went to look for a microwave, Leela actually said to the oven salesman "Yo Homes, we want a microwave oven." She thought that's how all people from any decade of the 20th century talked. Fry learned that the waitress at the restaurant was his grandma. He took his grandfather to where nothing dangerous can happen so he took him to a house in the middle of nowhere. Unfortunately, the house was being used for nuclear bomb testing, so his grandfather was killed, but he still existed. He went home with his grandma and ended up having sex with her. The next morning, the professor told Fry that he was his own grandpa. At the research facility, President Harry Truman told the scientists to take their alien research to Area 51. Someone commented that the fake moon landing was supposed to be there, and Truman said that they'll really have to land on the moon. They stole a satellite dish that powered by microwaves and used it to go back to the year 3000.

So instead of the grandfather paradox, time travel in this episode was actually a prophecy. The whole universe was dependent on them going back in time and Fry becoming his own grandfather, which explains why he's so stupid.

Oh, yeah, I heard about that episode. It sounds awesome! :)