Off-main-thread animations now enabled on all platforms for Nightly and Aurora ({{bug|980770}}). This means many animations of the transform and opacity properties will now run on the compositor thread, with fewer updates on the main thread.
=== Media ===
We shipped some MSE fixes in the Firefox 37.0.2 chemspill, so YouTube will re-enable HTML5 video for Firefox 37.0.2 on Windows next week.