I'd usually say that negatives should be addressed by you on your terms - i.e. you bring it up and tell them - but I think this is one where you wait until asked.
If you can rightly say it was a difference of opinion then do so.
If you were in the wrong, you just need to address it, turn it into a 'what you've learned / changed' kind of thing and hope for the best.
I think all of this is exceptional advice. Being able to be honest and convince a potential employer of your sincerity and ability to change are huge when talking to them. I think it's also a chance to look at the semantics of the issue. When I think of "being fired" I think of losing a job due to doing something vastly wrong or inappropriate. I know that other people think of any manner of leaving a job other than by their own choice as "fired". I guess I mean you may want to look at whether you were one of many people who lost a job, was the company downsizing, did they lose a contract, etc? That way you are really examining your culpability in losing your job.