OK, forget about my question.

I finally found out that making the library item from the web page, and then sliding the link to the pdf onto the newly creatied item did exactly what I needed...

oops

Edit: sorry, started writing before you posted again - most of it is still relevant though, and it should be even easier than dragging the link.

If you create the item from the web page (using the symbol in the Firefox address bar) it should add the PDF automatically if you tick "automatically attach associated PDFs and other files when saving references" in the preferences (gear menu -> preferences -> general tab). I've checked your link and it works for that article.

For any sites where this doesn't work you can drag any direct link to a PDF onto a Zotero item and it will attach the PDF to that item. You may also want to report the lack of automatic PDF saving, after searching the forum to see if it is a known issue, as the solution may be just a quick fix to the translator code.

Zotero doesn't really have any way to know what the title is—it just gets plaintext from the PDF, and whitespace isn't a very reliable guide. As far as I can tell, the problem with this document, with Zotero's current implementation, is that 1) there's no DOI and 2) the first page of author footnotes—particularly what comes through pdftotext (which you can see by examining the hidden .zotero-ft-cache file in the directory)—passes Zotero's test for body text, and so it queries Google for a bunch of universities and addresses.

It should probably try grabbing text from a few pages in—at least as a fallback—rather than just trying different passages from the first page that looks like body text. For what it's worth, many phrases in this paper don't appear to return results when doing a quoted search on Google Scholar, so it's possible Google indexed a different version.