I wonder whether this is the 32-bit/64-bit issue. Could you check this thread and see whether that makes any difference for you: Firefox does not play netflix.

Problem was solved by moving the previously downloaded version of Silverlight to the trash, emptying the trash, then downloading Silverlight a second time.

I had this problem Netflix too. Here's a sure fix for MAC users:

1. Access your hard drive (double click the hard drive icon in finder)
2. Find the silverlight plugin (navigate to your Internet Plug-Ins directory: /Library/Internet Plug-Ins/)
3. Remove the silverlight plugin (drag any of the following into your trash bin:

      * Silverlight.plugin 
      * WPFe.plugin

1. Empty your trash bin
2. Go to www.microsoft.com/getsilverlight/ using your Firefox browser.
3. Download and install silverlight
4. Restart Firefox

This removes a bad install of Silverlight and starts fresh. Definitely works!

I am using Windows 7 64bit Ultimate and for some reason I had a problem that I have seen many people on here was having and was blaming Firefox's Plugin Container when watching Netflix or anything using Microsoft's Silverlight. But it isn't the Container that is causing the "Silverlight Plugin Has Crashed" problem. I just talked to Microsoft about it and found the solution on fixing it. The problem is the Computer Browser.

You go to "run", then type in "SERVICES.MSC" when that pops up scroll down to "Computer Browser" highlight it then in the left hand side at the top you will see "Restart the service". That's it. Restart computer. Now Firefox will play Silverlight.

I have read so many posts about this with people coming up with all sorts of things to try to fix this, but none has worked....for me anyway.

So do this and I'm sure you'll be happy again.