When researching or visiting a website or page, it may be useful to ensure that there is a copy of it saved from that date, which is accessible on an Archive site, such as at Archive.Org or Archive.Today. To do this, both sites have areas where you can post a URL, to have it saved and archived at that time, with those pages being available Here for Archive.Org and Here for Archive.Today.
As always there are some useful Add-ons & Extensions, which can make this an easier process, by adding icons to your tool bar (and available via a Right Click), which can be selected when on a website or page of interest, which causes it to be sent straight to the archive site for archiving. With Add-Ons / Extensions for Archive.Org available on FireFox & Google Chrome, and for Archive.Today available on FireFox & Google Chrome.