From the tool bar of the reply window, you will see the Youtube icon...
CLICK on that and a message will prompt, "This website is using a scripted window to ask you for information. If you trust this website, click here to allow scripted windows..."
RIGHT click it to Temporarily Allow Script Windows..., then
CLICK on the Youtube icon again...
A small window called "Explorer User Prompt" will pop up at the left hand corner...
COPY and PASTE scripts "ZamIYtAoZ-g" into the prompt window... and that should do it!