The Internet Archive is a non-profit library founded in 1996 to provide Universal Access to All Knowledge. Its Wayback Machine explores more than 305 billion web pages saved over time, and allows web pages that no longer exist to be retrieved, or current web pages to be archived for posterity. See https://archive.org/about/ for further details.
Browser add-on extensions allow the Wayback Machine archive of missing web pages to be easily retrieved.
In Firefox browser use Tools > Add-ons and search for Wayback Machine for available extensions.
In Chrome browser use Tools > Extensions and search for Wayback Machine for available extensions.Link: Internet Archive Wayback Machine