Related: I used to keep a collection of locally mirrored web pages a long time ago, with a legendary Firefox extension called ScrapBook [0] (now long retired). The surprise for me is that after all these years I still remembered the name...

While writing this comment I found that it lived on as a (now "legacy") new extension named ScrapBook X [1], and then yet another one named WebScrapBook [2], which seems to still be alive!

[0]: http://www.xuldev.org/scrapbook/

[1]: https://github.com/danny0838/firefox-scrapbook

[2]: https://addons.mozilla.org/en-US/firefox/addon/webscrapbook/