Firefly was cancelled because no one watched it. That is the answer to the million dollar question. It was not because of some correct order nonsense. It was not because of some executive meddling. Nor was it because the target audience went out on a Friday night.
Did it deserve to be cancelled? In my summation, yes it did. The show forgot to have a goal it was building up towards. I can tell you that there were a ton of shows took the same amount of episodes and remembered to have a compelling storyline, interesting characters, and a coherent vision.
The main problem with the show is the not clever dialog. I hate cutesy self referential dialog.