Yeah but if the site issues a 404, you simply right click and the extension will show you the archived copy. Sadly many sites fail to provide a decent 404 page if a resource doesn't exist, they just do redirect spamming or in the worst case: 503 error[0]

(But I understand your need for text search on these services)

[0] https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/503