In "Fahrenheit 451", how has Montag changed over this novel and how did his beliefs and actions change by the end?

Montag goes from being a good citizen of their society wholoved his job.  He states that "it was a pleasure to burn"; he wanted to "shove a marshmallow on a stick" in front of the burning house, and went to bed with a "fiery smile still gripped by his face muscles."  He took the exact pleasure in his job that his society hoped he would.

He starts to change when he meets Clarisse.  For the first time in his life, questions whether he is happy.  His safe world had "melted down and sprung up in a new and colorless form."  From here on out, he starts questioning things.  He starts asking questions about the people whose houses he burns.  And, the next house he burns, instead of wanting to callously toast marshmallows, he is highly disturbed.  He goes home and can't sleep, then stays home "sick"; he suffers a crisis of sorts.  He confronts the Barbie-esque Mildred and her friends.  He seeks out Faber, and they make plans for rebellion.  He starts openly reading books, defiantly insisting on taking them in.

At the end of the novel, his entire world has changed; "he would not be Montag anymore...and one day he would look back upon the fool and know the fool.  Even now he could feel the start of the long journey, the leave-taking, the going away from the self he had been."  He finds the courage to run away, and with others, try to rebuild things in a better way.