Plugins and Internet for New Macbook

I just got a new Macbook and I am loving it. I have just about everything set up on it. But when i was looking online via Firefox it came up to an invaild plugin error. I was trying to look at a video and it said that there was no avalible plugin but when i tried it on my windows machine it worked fine. I was just wondering if there were some plugins or downloads i need to do so that i can view video off the internet.

www.flip4mac.com has the wmv plugin for windows media files. It just came out last week.

Thanks i'll see if it works, that is the one i have been looking for