It's not a plugin problem at all, but a couple of missing .dll files.
You need to insert two files into your FireFox "plugins" folder in Programmes Files > Mozilla Firefox > Plugins. They are: npdsplay.dll and npwmsdrm.dll. They can be found by a quick google and copy and pasted into your plugins folder.
Thought I'd put this up so if anyone else had the same problem heres the fix.