Mozilla Firefox/Platform Engineering Update 39.3

This engineering update is also available on the Platform/2015-04-14 wiki.

Firefox Release Schedule (lmandel)

  • We shipped a Firefox 37.0.1 desktop and mobile chemspills last week.
  • Firefox 38 Beta 1 shipped last week.
  • Updates have been re-enabled for Aurora.
  • 5 weeks until the next merge date (2015-05-11).

Upcoming Outages (hwine)

Tree Closing Window on Saturday April 18 for at least 4-5 hours of work (time TBD). Tracking bug 1151645.

MemShrink (njn)

Brian Hackett took advantage of the removal of object parents to reduce the size of base shapes (bug 1143256). The JS engine creates many of these to track the characteristics of JS objects.

Nick Fitzgerald greatly reduced the amount of memory used for saving JS exception stacks (bug 1038238). This reduced the memory of a test case compiled from Dart to JS from over 1GB to around 170MB (bug 1125259). For implementation details, see Nick’s blog post “A Compact Representation of Captured Stack Frames for SpiderMonkey”.

Seth Fowler fixed a bad leak regression (bug 1150127) where closing a page while it was in the process of loading could leak the page and cause long browser pauses. Seth also fixed a pair of issues that caused very large memory usage (more than 1GB) when scrolling in the downloads list (bug 1148682 and bug 1148684).

Bill McCloskey fixed an issue where a docshell was being held alive for too long on e10s (bug 1137933). This was one of the remaining blockers to enabling e10s Mochitest browser-chrome tests, which will give us more test coverage for leaks.

Media (cpeterson)

We shipped MSE (Media Source Extensions) for YouTube in Firefox 37 on Windows Vista+. Unfortunately, we discovered multiple unrelated issues in the release channel that all manifest themselves as “video is black”:

YouTube helped us quickly revert all Firefox users from HTML5 video to Flash. Once the problems were identified, YouTube was able to switch OS X and Windows Vista+ pre-channels back to HTML5 video. We plan to ship MSE for YouTube on Windows Vista+ in Firefox 38 (or 37 if hotfix bug 1152630 is released soon) and on OS X in Firefox 38 (or possibly slip to 39).