I do wonder though, is this performance improvement Windows specific? It's hard to believe that Mozilla could make up the difference in only three or four months.
Edit: looks like Chromium still beats Firefox on Linux: https://treeherder.mozilla.org/perfherder/graphs?highlightAl...
In fact, all benchmarks browsers seem between a quarter and a third slower on Linux in speedometer. That's strange, I wonder if this has to do with the limited availability of hardware acceleration?