Firefox/Platform Engineering Update 39.2

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Firefox/Platform Engineering Update 39.2

Chris Peterson-12
This engineering update is also available on the Platform wiki:

# Firefox Release Schedule (lmandel)

We shipped two chemspills over the weekend: Firefox 36.0.3 and 36.0.4
(plus Firefox ESR 31.5.2 and 31.5.3)

Firefox 37 is scheduled to be released on March 31. That's next week!
For Firefox 37 Beta/Release, please report any keyboard related issues
on OS X such as the keyboard stopping to work and requiring a browser

# MEM SHRINK (njn)

jemalloc3 has been disabled again on trunk due to Windows crashes. The
heap allocator is a fundamental thing and changing it in a complex
program like a browser is hard.

Thanks to Jim Blandy, jemalloc (the old version currently used in
Firefox releases, not jemalloc3) is now used as the allocator for the
JavaScript shell, instead of the system allocator (bug 1134039). This
makes the shell configuration closer to the browser configuration, which
will make results more representative. But we don't yet
have data on whether those results have changed significantly due to
some OS X problems (bug 1146267). It's worth repeating: changing the
heap allocator is hard.

about:memory now has a "resident-peak" measurement (bug 1145007) on Unix
(Linux, OSX, *BSD), which measures peak physical memory usage for the
process. It may be useful for detecting short-lived spikes in memory usage.

The new Reader View feature was causing high memory usage on desktop
Nightly, but has been fixed in bug 1139678.


In Firefox 37, the Media team is shipping the MSE API (Media Source
Extensions, bug 778617) to improve YouTube's HTML5 video playback on
Windows. YouTube will now default to HTML5 video instead of Flash on
Windows. MSE for OS X is being tested in Aurora 38.


The Shumway team continues to focus on improving startup performance and
Flash ad rendering.
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Firefox/Platform Engineering Update 40.1

Chris Peterson-12
This engineering update is also available on the Platform wiki:


We shipped a Firefox 37.0.2 chemspill which added some old Intel GPUs to
our GPU blocklist.

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.

# MEDIA (Chris Peterson)

We shipped some MSE fixes in the Firefox 37.0.2 chemspill, so YouTube
will re-enable HTML5 video for Firefox 37 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

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:

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).
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