Screenshot / demo
Inspired by the Meta Stack Exchange question Automatically have links archived in the Wayback Machine. This script searches the post for external links and offers a simple way to archive them in the Wayback Machine, so that future readers will be able to access any additional information (context for quotes, recommended reading, etc.) even though the links may break.
developed & tested with Violentmonkey on Firefox
You can hover over the link to see what will be archived; if none are found, the link will be grayed out: