Change in the way e10s and multi are enabled on Nightly

Blake Kaplan mrbkap at
Wed Oct 18 18:52:41 UTC 2017

Hello everybody,

I'm in the process of landing a change in bug 1406212 [1] that changes the
way that we handle enabling or disabling of e10s and e10s-multi. This
change will ride the trains, so Firefox 58 will be the first version with
the simplified logic.

To recap the current situation: we have 4 prefs that control these
features: browser.tabs.remote.autostart, browser.tabs.remote.autostart.2,
dom.ipc.processCount, and dom.ipc.processCount.web. On Nightly,
browser.tabs.remote.autostart.2 defaults to true and dom.ipc.processCount
defaults to 4. On Beta and Release, they default to false and 1
respectively. We then update these preferences via the e10srollout addon.
This has been the cause of much confusion and several bugs.

As of today (assuming the patch sticks), these features will be controlled
by the prefs browser.tabs.remote.autostart and dom.ipc.processCount. They
default to true and 4, respectively and behave as one would expect.

One more thing to point out: with the removal of e10srollout, I also
removed the code that would disable e10s if we detected a
non-multiprocessComptaible extension. We are entirely relying on the addon
manager to refuse to install such extensions.

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