Links, when outputted to the chat, do not work

Reproduction techniques:

1: Join a server under 17w45b.
2: Put a link into chat. Any link will do.
3: Clicking the link does not bring up the window that says "would you like to open this external link?", nor does it automatically open.

What should've happened:

The "would you like to open this external link" window should show up.

What happened:

It did not show up.

My chat settings should make this happen, attached below.