This episode is considered non-canon and the events featured do not relate to the series and therefore may not have actually happened/existed
Simpsons Christmas Stories is the ninth episode of The Simpsons' seventeenth season. This is one of several Simpsons episodes which are considered anthology episodes that features mini-stories.
It's D'oh-Ho-Homer with these three Christmas stories: "The First (Annoyed Grunt)-El" when Reverend Lovejoy can't get to church to deliver the Christmas sermon because of a train wreck (a model train wreck, that is), he asks Ned to deliver it, but when Ned gets a paper cut, it becomes The Gospel according to Homer, with Marge as Mary and Bart as Jesus. "I Saw Grampa Cussing Santa Claus" - in a World War II flashback, Grampa and Mr. Burns become standed on a deserted island where Burns shoots down Santa Claus. "The Nutcracker...Sweet" - to the music of Tchaikovsky's ballet, everyone prepares for Christmas in their usual way, including Moe trying to kill himself and Homer forgetting to buy Marge a present. 
The First (Annoyed Grunt)-El
When Reverend Lovejoy can't attend the Christmas sermon due to his train set catching on fire, Flanders immediately takes over.
However, he gets a paper cut and faints. Homer plans to lead the sermon and tells the story of the first Christmas, with Marge as Mary, Homer as Joseph, Lisa as the angel Gabriel, Mr. Burns as King Herod, and Bart as Jesus.
Mary tells Joseph that she is pregnant, even though she's a virgin. The angel Gabriel appears to them and explains that Mary is going to give birth to the Son of God. The three wise men (Dr. Hibbert, Principal Skinner, and Professor Frink) tell King Herod that they are going to give gold, frankincense, and myrrh to the King of the Jews. When Herod thinks that the gifts are for him, the men explain to him that they're for the baby Jesus. Herod becomes furious and claims that he will kill the baby.
At the Bethlehem Inn, the innkeeper (Moe) tells Mary and Joseph that he has plenty of rooms available with brand new carpeting. However, when Mary's water breaks, he forces them to stay in the barn. Mary successfully gives birth to the baby, and the three wise men, along with the two shepherds (Lenny and Carl) come to see Jesus. Joseph is upset because he isn't Jesus' father, and when he drinks some wine, the baby turns it into water.
When Jesus keeps crying, Mary gives him to Joseph. He entertains him by hurting himself and one of the wise men (Skinner). When Jesus finally falls asleep, Herod and his troops find the manger that they're staying in. They escape and trick the soldiers by putting Jesus' halo on a duck. On top of the hill, Joseph cuts down a pine tree, and as it rolls down, the soldier gets caught in it. The soldiers, along with Herod, are arranged like ornaments on the tree, and the duck, still wearing the halo, stands on top of the tree. Mary calls it a Christmas tree, and Homer concludes his service.
I Saw Grampa Cussing Santa Claus
When Bart and Lisa find Grampa trying to stick a bear trap on top of the chimney, Grampa tells them that he's trying to get his revenge on Santa Claus. Bart asks why, and to their dismay, Grampa tells them one of his many stories.
Back in World War II, Grampa and his brother Cyrus (never mentioned until now) were serving as Navy Pilots on an aircraft carrier in the Pacific; fighting off a Japanese kamikaze attack when Cyrus got shot down due to the fact that Lieutenant Montgomery Burns, Abe's Tailgunner, refused to radio Cyrus because he was busy talking to a girl on the plane's radio. Shortly after, Abe and Burns also get shot down and are stranded on an island. Burns tries to assert dominance stating that on the island military rank means nothing, and that the strong of will control the weak. Abe, however, the commanding officer, is not threatened by this and quickly overpowers Burns, asserting his own dominance, by dunking Burns' head repeatedly in the ocean. They eventually settle their differences. After a few months, on Christmas Eve, they see a plane in the sky, and Lt. Burns shoots it down. However, when they go over to investigate, they see that it is actually Santa Claus. They build him a new sleigh using the parts from the plane and they gather up all the presents. When Santa was about to leave he was missing Prancer and Rudolph the latter shown to be in a snake. Lt. Burns knocks him unconscious with a coconut and flies away in the sleigh and claims that he is going to keep all the presents, because at heart, he's just a very wicked child. Grampa catches up to him on Prancer and jumps on board the sleigh. After he beats Mr. Burns with a tricycle, stating that someone should have done that years ago, and Abe gives the sleigh back to Santa. As Santa leaves, he tells the young Grampa that he'll be back in a few days. As Santa flies away, Abe states that it was the craziest thing he had ever seen. Immediate after, a nuclear test explodes at nearby Bikini Atoll, causing Abe to re-state his previous claim about the rising mushroom cloud. Santa Claus however, never comes back and Abe then claims he had to get off the island using a jet ski he made out of coconuts.
Bart and Lisa believe that it's just another one of Grampa's far-fetched tales, but when they hear a thump in the den, they find that Santa is there. He tells them that Cyrus didn't die, but instead crashed into Tahiti. Santa takes Grampa there, and they meet up with Cyrus and his fifteen wives. Santa explains to Grampa that he didn't come back for him on the island due to his procrastination and eventually feeling embarrassed about it.
After the children of Springfield Elementary perform The Nutcracker, everyone begins to go along their day singing to the tune of the songs from the play. This is done after mentioning that the songs in The Nutcracker are in the public domain and thus can be and are played constantly for free. Homer told Grandpa that they weren't going to be at home and hid when he came, forcing Grandpa to spend his Christmas in the dumpster with raccoons, who got Grandpa some rancid lard. Krusty then shows a clip from The Krusty Show from 1964 where Krusty had snowballs thrown at him from the audience and with John Glenn and Dr. Martin Luther King, Jr. as guests. After the opening number, sung to the tune of"Marche", Moe continues his annual holiday tradition and attempts suicide thrice, and naturally fails, done to the tune of "Dance of the Flutes". Moe first tries to hang himself firstly with string popcorn which breaks. Secondly he rides a sleigh through traffic with a note saying No one gets my organs pinned to his chest but isn't ran over Moe then tries to shoot himself with a gun but this turns out to be a comedy bang gun saying Merry Christmas. Finally Moe then asks Barney to kill him who refuses on the grounds that he had brought him a wool hat.
That evening, Marge tells Homer that he'll like the present that she got him. Not wanting to upset her, Homer tells her that his present for her is outside and drives away to buy her a present, sung to the tune of "Trepak". Every store is closed, and all Apu has at the Kwik-E-Mart is some jerky made out of trout. Homer searches in garbage cans, gutters, trees, and he even chases down Milhouse, but he can't find anything.
When he gets home, Marge gives Homer his present, done to "Pas De Deux". He opens it and sees that it is another present with a tag that reads, "To Marge, From Homer." Marge tells him that she knew that he would forget to give her a present, so she gave him one to give to her. He gives it to her and she unwraps it, and Homer sees that it is a picture of him dressed up as Santa with Marge on his lap. They hug and kiss, and Moe, for the fourth time, attempts suicide by again riding on a sleigh in the road, and fails again after an eighteen-wheel semi missed him.