It's possible that the Silverlight browser plug in is disabled which means video playback might not work.
The below steps are a guide to ensuring silverlight is switched on in your preferred web browser.
Click on "Safari" in the menu bar and go to "Preferences".
Click on the "Security" tab (The Padlock Icon)
Locate Plug-ins Settings box at the bottom
Select Silverlight Plug In, in the left hand column
For 'When visiting other websites' choose 'Allow Always'
Press the Alt key on the keyboard.
Click the Tools menu at the top of the browser window.
Select Manage Add-ons.
Choose Toolbars and Extensions from Add-on Types, in the left pane.
Select All Add-ons from the dropdown menu, at the bottom of the left pane.
Click on Microsoft Silverlight.
If disabled, click the Enable button in the bottom right corner of the window.
Click on Firefox.
Select Silverlight Plug-in.
If disabled, click Enable.