HEY!  Just came back here to say you are right. Installed the developer beta of OS X 10.11 today (which includes Safari 9) and tried to open some of the output files from the old project mentioned above.<p>They all work in OS X Safari now.<p>None of them really stress-test flexbox or do anything advanced; they are just grids that are supposed to resize well. But, the bugs we hit doing this basic stuff in OS X 10.10 &#x2F; Safari 8 seem to be fixed.