This might be too specific and may not suit your needs, but I used ArchiveWeb.Page to download entire webpages without any of them breaking. You can record webpages and save them as a .warc file. You can open the .warc file using the ReplayWeb.Page app. Both apps are open source and are meant to be website archivers but also works great for this purpose.
I tried using extensions that can save a webpage as HTML/PDF/whatever, but that often didn’t save everything in the webpage and the downloaded copy is pretty much fully broken and useless.