This WayBackMachine extension is nearly mandatory on the modern web. There are so many pages nowadays that have disappeared or changed that I find myself constantly having to look up archived copies. This extension saves me the tedium of repeatedly copying a URL, going to archive.org, then pasting it into the search box.

There are some downsides, but this is such a needed feature that I have to give it five stars.

Downside 1: this extension adds yet another button to my already cluttered toolbar. I'd much rather that it showed up in the context menu (right click) and could be bound to keyboard shortcuts.

Suggestion: Perhaps the next version could implement both interfaces, but allow either to be disabled in the preferences.

Downside 2: this only checks archive.org. While that is my preferred site, other extensions also have the ability to check cached versions from Google, Coral, and other search engines.

Downside 3a: While this extension's ability to automatically detect 404 (not found) errors is a nice feature, it doesn't seem to work everywhere (try youtube.com/thisurlreturns404).

Downside 3b: Even worse, some websites don't like returning 404, and instead return 301 (moved permanently) or 302 (redirect). For example, try ebay.com/notfound, which redirects the URL to pages.ebay.com/messages/page_not_found.html?abigbunchofgarbage and then returns 200 (success). On a site like that, if you then click WaybackMachine → Recent Version, you'll either be told "URL not found in wayback archives" or be shown an archived copy of the wrong page.

Suggestion: Perhaps a future version of this extension could make note of redirections and, when the WayBackMachine is used, the requested URLs would be tried in FIFO order (until one of them succeeds or they all fail).

Downside 4: If the lookup at archive.org fails, an error dialog will pop up with an annoying alert sound.