Open gpedit. Then in the left navigation column, select
Computer Configuration > Administrative Templates >
All Settings.
In the right pane, scroll down until you find
Display mixed content.
(snapshot)
Double-click that entry, and its configuration page will appear.
Click the "Enabled" radio button, then choose the "Enable" option from the dropdown below.
(snapshot)
The filtering options are sometimes easier to use, rather than hunting and scrolling the right pane. It's kind of confusing to find the filtering options though. They are not present until
you first click Administrative Templates. Then look in the
View menu in the menu-bar across the top, and there they are. (snapshot)
