Have you https://addons.mozilla.org/firefox/addon/single-file/?

If you really just want the text content you could just save markdown using something like https://addons.mozilla.org/firefox/addon/llmfeeder/.

On the subject of SingleFile there is also WebScrapBook: https://github.com/danny0838/webscrapbook

I prefer it because it can save without packing the assets into one HTML file. Then it's easy to delete or hardlink common assets.

I see that it gives three choices for saving the assets: single file, zip or folder. Is the zip version just zipping the folder?