Hey all!

It's been a while (7 months!) since the first Fission newsletter, but we've
made some exciting progress we'd love to tell you about!

Enabling Fission on Nightly

It's now possible to turn on Fission in nightly builds of Firefox by
setting fission.autostart pref to true. Fission can also be enabled for
running tests using mach test … --enable-fission.

When Fission is enabled, each cross-site iframe is loaded in a different
content process, meaning lots of different processes participate in drawing
a single tab. The hover tooltip for a Fission-enabled tab is annotated with
a "[F …]" containing a series of process IDs, as shown in the image below,
serving as a visual verification of an active Fission-enabled session.

We currently do not recommend trying to use Fission for day-to-day
browsing, as there are still known stability issues. However, if you do try
it out, please file bugs/issues blocking fission-dogfooding

Fission Mochitests on mozilla-central

Fission Mochitests were recently enabled as tier-2 jobs on mozilla-central.
This will allow us to run tests with Fission enabled on infrastructure, and
prevent landing new features or code which don't support Fission. Tests
which do not currently successfully pass are marked as fail-if =
Fission or skip-if
= Fission.

We'd love your help migrating tests to run with Fission enabled! Here are a
couple of handy tips for making your test Fission-compatible:


   Use SpecialPowers.spawn(target, [args…], async (args…) => { … }), to run
   code in potentially cross-origin iframes, as they may be in a different
   process. This API is similar to the ContentTask.spawn API used by
   browser-chrome mochitests.

   Wait for document loads to complete before trying to run code inside the
   target window, as a process switch may occur after the frame or browser is
   created. For frames in content, this usually means waiting for the load

These tests may also be run on the tryserver, however they are currently
excluded from the default set. They are called M-fis, and can be found
in ./mach
try fuzzy --full.

Fixing these Mochitests is a goal of our next major milestone, M4! There's
a ton of awesome stuff happening in M4, which you can read about on the
wiki (https://wiki.mozilla.org/Project_Fission#M4_goals).

Fission Talk and Demo

At the 2019 Whistler All-Hands, Nika gave a talk & demo about the Fission
architecture. This talk is publicly available on Air Mozilla.

You can watch the talk here:

The slides are here:

And… So Much More!

A ton has happened in Fission over those 7 months, and it would be
impossible to cover all of the awesome work everyone has been contributing
to make Fission happen. We just want to say a massive thank you to everyone
who has helped with Fission - writing patches, doing reviews, planning, and
more! We hope to do brief update newsletters like this one with a better
cadence, so hopefully there'll be another one of these in your inbox soon.

Let's keep fission-on!

- The Fission Team.
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