Version 3.0 works fine here!
With the new feature, which shows saved status of the page right away, now it is very easy to make a decision whether or not to save the page. To do this with prior versions, I had to first check the newest saved page and to see if it exists or not. The saving process is being done in background, so I can browse other pages while the add-on saves a page.

(Below is my review a year ago about previous version)
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Once worked fine, but for the past few months, it has got "Fail with status: 498 No Reason Phrase" error with Retry button, which fails all the time on firefox (waterfox as well). So, now this extension is quite useless and needs to be updated.

Finally, they fixed this and it works perfectly.

The good: if it works, it works. It's an amazing tool to save webpages and look them up if necessary.

The bad: the 404 page has always come up too soon but lately (1-2 weeks ago) webpages cannot be saved. The error message: job failed.
No one can do anything with that information.. saving a page directly from the website works but if I cannot save a webpage with this Addon why should I keep it?

I have found all functions of this add on, including archiving pages, detecting dead links and requesting archived pages to be entirely non functional. It prevents me from accessing working sites so often that I finally relented and uninstalled the add on

Too often it misdetect a perfectly fine website as "not found" and redirect to the addon page.

High failure rate. Needs fixing. Great when it works! I just wish it worked reliably. Too important a tool to be this unreliable.

Mozilla Firefox 96.0b6 (64-bit) — версия 1.8.6 дополнения грешит частыми ложными срабатываниями на живых, доступных вебстраницах. В настройках дополнения нет возможности включить отображение на страницах со снимками веб-страниц верхней панели с временной шкалой.

Would be a perfect addon without this feature: "Detects dead pages, 404s, DNS failures & a range of other web breakdowns", beacuse often when I go previous page or Ctrl+Shift+T, this addon popups, blocking the page loading properly.

EDIT: It was finally updated, and although it still is susceptible to false positives, it's greatly improved and extremely useful now!

Same complaint as everyone else: this addon would be SO useful if there was some way to dial down the sensitivity of the automatic redirect or turn it off — but since the addon hasn't been updated since 2018 I assume this bug won't be fixed. Hopefully someone picks up where they left off and implements this functionality into a working addon, because it's a great idea.

Very useful when I need it, but it constantly triggers if a page is loading even remotely slow. Always triggers during cloudflare ddos protection pages.

Not only is it incapable of archiving any web page, but it also gives so many false positives when it thinks a site is down when it in fact is not.

Means well but just kicks in too quickly and too often.

Same issue as everyone else. You *cannot* throw a splash screen in my face every time a page fails to load properly. Have some respect for your user base - if someone is familiar with the Wayback Machine and chooses to install this extension, chances are they know how to navigate to the archive for dead pages via the widget! Please add a toggle. This is an issue I would have expected the Archive Team of all groups to be savvy to.
My primary reason for downloading was to be able to quickly save websites and contribute to the archive. While this extension makes that slightly more convenient, I would recommend that anyone seeking similar functionality just memorize this to prepend to the address of whichever page you want to save: "https://web.archive.org/save/". If you're more interested in the other function, you can instead prepend "https://web.archive.org/web/*/".
Other people have suggested that the page-down screens be converted into banners, and while this would be a huge improvement, I would really like to be able to disable all popups regardless of "intrusiveness." Again, this seems like something you guys would be sensitive to! I can't understand why it's designed this way.

Can't use it: detection of down webpages gives too many false positives. And it messes with browser's history replacing original URL so you can't just click "reload" or "back" to get back to original URL. Have to uninstall.

The new v3 is very good