It's worth keeping a few points in mind when reading these results:
1. The survey was carried out in October 2017. Things can and do move quite rapidly in this area, especially given the increased number of users who will be running Windows 10 now who may not have been back then.
2. IE won't be around forever, and once the accessibility of Microsoft Edge improves (which is likely to happen pretty soon when they adopt Chromium), IE will become less and less relevant.
3. NVDA with Firefox is a much more common combination than JAWS with Firefox, primarily because the NVDA developers recommend it. Freedom Scientific (makers of JAWS) have historically pushed IE perhaps more than other browsers, so it will be interesting to see how that changes as Edge becomes more usable.
IE is mostly used here because it works best with the screenreaders, not because it's preinstalled or other common reasons. When I test with IE, and then with Firefox, I notice subtle things with big impact working better in IE e.g. I found that screenreaders are particular better with multilingual content on IE. I can't recall the exact screenreader/browser combo, but on IE, I got proper support for different voices for different languages when an element other than the HTML element had a lang attribute.
[1] https://webaim.org/projects/screenreadersurvey7/#browsercomb...