Wayback Machine for Firefox
This is a microscopic extension for Firefox, adding a button and a context menu item for interacting with Archive.org's Wayback Machine service.
Open In Wayback Machine Button
Clicking on a button opens the currently opened page in Wayback Machine.
It is immensely useful in situations where you open a dead link and are presented with 404 "Not Found" or no host whatsoever. In such a case you can just click a button and see if Wayback Machine has crawled this link before.
Wayback Machine Context Menu Item
Any link on a webpage can be opened directly in Wayback Machine. This can be useful when you know beforehand that you are navigating to a dead link.