For some reason, I can no longer download multiple citations from JSTOR -- in some cases (realized this as I was writing this; see links to example functioning and non-functioning pages below).

I'm on OSX 10.11.4 and Firefox 46.0.1 (I'm fairly sure this problem started with FF 46, though can't swear to that).

In the problem cases, on the page where JSTOR lists search hits, the Zotero folder icon does not appear, and clicking on the page icon results in the results page being saved as a web page.

Saving individual articles from their own pages in JSTOR works just fine, including downloading the PDF.

This problem does not affect e.g. Google Scholar citations; on the Google Scholar search results page, the folder icon does appear and clicking it works as expected (it seems to work every time as far as I can tell).

The problem appears, for example, with this JSTOR search:
http://www.jstor.org/action/doBasicSearch?Query=labor&acc=on&wc=on&fc=off&group=none

This JSTOR search, by contrast, displays the folder icon properly:
http://www.jstor.org/action/doBasicSearch?Query=%22knights+of+labor%22&prq=labor&group=none&fc=off&so=rel&acc=on&wc=on&hp=25
Clicking on the folder icon works as expected in this case.

On Google Scholar, both produce correct results, e.g. here:
https://scholar.google.com/scholar?hl=en&q=labor&btnG=&as_sdt=1%2C6&as_sdtp=

Thanks for any help!