Ok. This extension used to be *bad*. It was limited in its use and had a serious problem with what I'm terming "archive misfire", where it would decide to redirect some pages (which would otherwise load just fine!) to a new page where it gave you the option to view it in the archive. When you didn't need to.
Yet now! As of February this year, the extension has leapt all the way from version 1.8.6 to version 3.0, and let me tell you, this version absolutely slaps. It's brilliant. Archive misfire is no more, and it's got all sorts of helpful little options. The Internet Archive has taken this extension from an over-agressive bookmarklet to a really quite helpful browsing tool. If you scorned this extension before, I invite you to give it another go; and if you're here for the first time, don't be scared off by the review score - truly, things are better now. Also, some other reviews mention needing to login to save pages, a requirement which has been lifted as of ~a month ago.