Is there a way to – outside of EagleFiler – save web pages in the web archive format? (To one’s desktop, say?)
You can use File > Save As in Safari. Or Option-drag an existing Web archive from EagleFiler to the desired folder.
web archive
Are any of the Firefox options webarchive-like? (They don’t seem to be.)
No, I don’t think the Mozilla browsers have anything like Web archives.