There&#x27;s an existing add-on that (kind of) does this. It checks Google Cache and Internet Archive, among others.<p><a href="https:&#x2F;&#x2F;addons.mozilla.org&#x2F;en-US&#x2F;firefox&#x2F;addon&#x2F;resurrect-pages&#x2F;" rel="nofollow">https:&#x2F;&#x2F;addons.mozilla.org&#x2F;en-US&#x2F;firefox&#x2F;addon&#x2F;resurrect-pag...</a>