Try not using Normalized lights. In most of my tests, I get rid off fireflies by turning off this option, and cranking up the light intensity to compensate.
More a workaround than a real fix, but there must be something broken with normalized lights at the moment.
I will try that next. I am having a little luck with limiting dynamic range... but I actually thought that had to do with GI, which I'm not using. Just a bright backdrop color