This engineering update is also available on the Platform/2015-04-24 wiki.
Firefox Release Schedule
Only two weeks until the next Firefox release: 2015-05-11!
Layout (David Baron)
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.
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.
Performance (Vladan Djeric)
Aaron Klotz and Ben Turner paid a visit to Adobe’s Flash team at their SF offices. They were able to provide fixes for several Flash player issues! An example of their work is in bug 1133351. This particular patch also landed in our codebase.
Many Telemetry histograms automatically expired in Nightly 40. Check Histograms.json and bug 1156565 to see if your histogram needs to be updated.
Telemetry unification work is continuing, Phase 3 is tracked in bug 1120356. Enabling unified Telemetry (i.e. FHR + Telemetry) might get pushed back to Firefox 40.
Among the latest Telemetry changes, Telemetry will submit data more aggressively to make analyses more reliable (akin to FHR) and to reduce reporting latency. Additionally, unified Telemetry now archives Telemetry data on the client for 6 months — this archive will be used to power the Firefox Self-Support feature.
Yoric added a “Task Manager” feature to Nightly 40 (bug 674779) to identify tabs and add-ons that are consuming the main thread’s time and slowing down Firefox. Specifically, it reports the time spent by the main thread inside different JS compartments. You can see a very rough UI for this feature by opening about:performance in Nightly. For overhead reasons, the feature currently does not measure time spent in compartments belonging to Firefox’s own chrome JS code.
The Performance team, alongside Platform teams, will be studying page scrolling & page navigation performance on desktop & Android in Q2: https://wiki.mozilla.org/Firefox/Content_Performance_Program
The Places database work done by the “Forget” toolbar button, the “Forget Site” history-menu feature, and the “Clear recent history” feature has been moved off the main thread (bug 1076775). Less jank!
If you notice any plugin issues (crashes, videos not loading, etc), please file a bug and mark it as blocking the async plugin initialization feature (bug 1116806).