Please pardon me if I'm the last to realize this, but it was all news to me. A few days ago I came across this link in a post over at CA:
http://www.digitaltrends.com/home-theater/getting-hd-netflix/#ixzz4Emz4P3OzIn the article they gave the maximum resolutions of several different browsers...
Google Chrome: up to 720p
Firefox: up to 720p
Opera: up to 720p
Safari: up to 1080p (on Macs running OS X 10.10.3 or greater)
Microsoft Edge: up to 1080p
Internet Explorer: up to 1080p
Since my Mac Mini runs OS 10.10.5 I used Safari to access my HULU account and discovered that I was now able to view the streaming video in 1080p instead of the 720p resolution that I was viewing with my Firefox browser.
It didn't take long before I decided to open up JRiver MC20 to see if I would have any luck in accessing my HULU account even though I hadn't been able to do so in quite some time. I set Safari as the default browser and much to my joy after I entered my HULU password in MC20 I was able to access my account for the first time in a very long time! I think that the reason for this current accessability may lie in the fact that HULU recently radically redesigned their website which includes a new feature called Watchlist and it may be that along with these changes it has become possible for JRiver MC to now be able to have full access to it's contents. I have since upgraded to MC21 and I am now enjoying HULU content in a much higher resolution that was not available to me when using the Firefox browser while JRiver MC was being denied access to HULU.