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

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. They all work in OS X Safari now. 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 / Safari 8 seem to be fixed.