Ytdyklly

Since Firefox 47 multi-process option Electrolysis (e10s) is enabled, but I am afraid, my Firefox still only uses one process.

There are a lot of options fingering with this subject in about:config:

browser.tabs.remote.autostart

extensions.e10sBlockedByAddons

extensions.e10sBlocksEnabling

How can I verify that all options are set right?

Which options enable/disable the multi-process capability?

How do I find out if an Addon blocks this option?

Open the site about:support in Firefox, which indicates if e10s is enabled.

There is a line "Multi-process staged rollout", which would be set to true if e10s is enabled. Also look for a number higher than 0 in the "Multiprocess Windows" entry (this is translated to your locale, e.g. "Fenster mit mehreren Prozessen" and "Web-Inhaltsprozesse" in german).

e.g., accessibility, add-ons can trigger disabling this feature.

On this site you can check, if add-ons, you are using are compatible: http://arewee10syet.com/. There is also a mozilla site to check compatibility, you find the addon-id in the extension-filenames in your profile folder, for example the "Tab Groups" add-on has the id tabgroups@quicksaver and is incompatible with e10s.

If you would like to opt-in to test the feature anyway, open about:config and toggle browser.tabs.remote.autostart to true. On your next restart, e10s should be active.

Force Enable

If you've tried enabling e10s but about:support indicates that e10s is disabled (e.g., accessibility, add-ons can trigger this), you can force e10s on for testing purposes. Within about:config create a new boolean pref named browser.tabs.remote.force-enable and set it to true. This is not encouraged, use it at your own risk!

(I tried it anyway and it worked, even with Tab Groups Addon still enabled but it's risky!)

Source: https://wiki.mozilla.org/Electrolysis#Force_Enable

My configuration is:

browser.tabs.remote.autostart : true

extensions.e10sBlockedByAddons : false

extensions.e10sBlocksEnabling : true

After these setting my about:support is showing that multiprocess Windows is enabled by user(me).

The first two options
browser.tabs.remote.autostart and extensions.e10sBlockedByAddons is important and third extensions.e10sBlocksEnabling doesn't seems to affect much. One important point is that extensions.e10sBlockedByAddons : false may break some of your addons.

I opted out of multi-processing in version 64.0.2 of Firefox by going to about:debugging#workers and click Opt out of multiple content processes:

I didn't make a mental note of which config option it was changing, and once opted out, there was no button to opt in!

Fortunately, I found the config value: dom.ipc.multiOptOut. The value should be empty.