Passive Cache uses Google’s text-only cache service and Archive.org Wayback Machine to display historical versions of a specified web link. This add-on allows for the viewing of a page, or site, while avoiding active connections to the target site.
Here are more details about this extension from the developers:
Upon installation, the extension provides additional menu items when you right-click upon a web link. You can then select either a Google Cache query or an Archive.org query.
This product was developed while training online investigation techniques to law enforcement, as it greatly met their needs. It has since found a home with users from all walks of life.
Interested in learning more? You can pick up Passive Cache from the Firefox Add-ons website.