Installing Silverlight on a Mac?

Some of my nursing classes require me to watch videos online, and the videos require Silverlight. I have installed it, uninstalled it, and searched forums until my head is about to melt. It will install and it says completed, says the software is installed, but when I try to view the video, it still tells me that I have to install Silverlight. I'm running Firefox, and I know that my system meets requirements. I'm at my wit's end! Any ideas? I really do appreciate it!

View this post on my blog: http://travelnursesuccess.com/installing-silverlight-on-a-mac