Nov 2025 update: roughly a year or so ago this extension stopped working properly for some sites (displaying a mainly black page). In the past few months it has been working properly for the sites it failed on. So as far as I'm concerned it seems to be back to what I'd expect, despite not having been updated since 2019.

Posted c. 2017:
Comparing the Update Scanner for FF57, as of 21Nov17, with its predecessor: I much prefer the old version. The new version opens sites in a page of its own, with a name like "moz-extension://f79626ca- etc. etc.". If you click on a link in the page it no longer works; on seeing a list of changed files, you can't click on any of them. This is a major issue for me.

It was convenient, with the sidebar opened, to click there to scan all pages. There may be ways round these issues, but they're not obvious. A nuisance, not major. I usually scan manually, setting the automatic scan to once weekly.

As many have commented, the scanner often reports pages to have been changed when there is no visible change; I expect that is unavoidable due to the nature of the pages, but is a nuisance.

On balance I still find the current version better than nothing; in particular I have a list of sites to remind me which to check. But it's got worse.