Why was Hephaestus crippled?

There are several answers regarding this topic.

(1) Hephaestus was thrown from Olympus by his mother, Hera, when she saw his unsightly face. As he fell, he was crippled by a ledge or was crippled by the landing.

(2) Hephaestus was crippled in his forges. When his mother, Hera, saw him as a cripple, she was disgusted. Repulsed, she threw her son (disowning him in the process) from Olympus.

All of the stories agree on what happens next:

When Hephaestus lands in the ocean, the ocean beings cared for him for many months - and possibly years. Some time during that time, he sought revenge on his hateful mother.

He sent her a golden throne. She, being extremely obsessed with perfection, loved automatically. However, when she sat upon it, she found herself unable to get up. Hephaestus had designed it to trap her.

The other Olympians realised what had happened and begged Hephaestus to return and free her. Eveventually, Dionysus (the God of Wine) sought out the spiteful Hephaestus and rendered him drunk. He then brought the unconcious God back to Olympus where he realised his mother.

Before he had a chance to leave, Zeus (his father) asked him to stay and work in his forges again. Hephaestus agreed, but was always quite cold towards Hera who acted the same in return.