To enable or disable an extension in IE via group policy:
First get the class IS of the IE extension by opening IE, clicking Tools (or the cog icon) and clicking Manage Add-ons. Click on the IE extention you want to enable / disable and click More information (blue text at the bottom). Take note of the Class ID
Open your group policy that is applying to the computer account that you want to enable / disable the IE extension on and navigate to: Computer Configuration\Policies\Administrative Templates\Windows Components\Internet Explorer\Security Features\Add-on Management
Enable the Add-on List policy and click Show
Enter the Class ID (including the curly brackets) as the Value Name
For the corresponding Value, enter a number 0 to disable the extension, 1 to enable the extension without the users being able to disable it or a number 2 to enable the extension and allow the users to disable it if they want
The extension will now be enabled or disabled in IE, depending on the option for the Value field that you entered.