How it works if the URL is pre-existing:

1. Select the footnote that contains a bare URL, such as http://www.example.com
2. See the "Convert" option in the context menu.
3. Click the Convert button.
4. Be happy.

How it works if I just added the URL:

1. Click Cite > Manual > Basic and insert a ref containing only a bare URL.
2. Realized that this is a mistake, and decide to try the citoid service.
3. Select the footnote to get the context menu. No Convert button.
4. Click the Cite button to choose Automatic. My URL isn't pre-filled, and it looks like it's inserting a second ref.
5. Be sad.

Desired result: Happiness. Also, less link-rot.