I've enabled e10s in Firefox 48. I checked this by going to about:support and I see this:
Multiprocess Windows 1/1 (Enabled by user)
I've also disabled all add-ons, but when I open 4-5 tabs I can see a single Firefox process.
Am I doing something wrong? Is there a variable in about:config that limits the number of processes to 1?
I'm using windows 7.
The accepted answer doesn't answer the question and is wrong. e10s can be enabled by the user, which is what the author of this question has done as indicated by the about:support output.
Multiprocess Windows 1/1 (Enabled by user)
If you're using Firefox 48 or later, you might be using e10s already. Check about:support and look for a number higher than 0 in the "Multiprocess Windows" entry. If you would like to opt-in, open about:config and toggle browser.tabs.remote.autostart to true. On your next restart, e10s should be active.
Now, back to the question at hand: The "Why" of Electrolysis
To ensure we don’t consume too much RAM, the first release of e10s will only use a single additional process for web content. We’ll add more processes in subsequent releases, as we become more memory efficient.
So to explain, Firefox is not using an additional process for each tab. Firefox, at the moment, is only using a single additional process to process web content. Eventually, as e10s evolves, it will be split further.
No, you are doing nothing wrong.
I've enabled e10s in Firefox 48.
Electrolysis is not enabled for all Firefox 48 users. At first only 1% of users will have it and later up to 50%.
In particular, users that are using extensions won't get Electrolysis enabled.
It appears that, depending on which add-ons/extension you are using, you may have to wait for a version of Firefox later than 50 (see later in this answer for the details).
This first phase of enabling our multi-process architecture is making its way to some of our Firefox 48 users starting this week. This is the biggest change we’ve ever made to Firefox, so we’re rolling it out slowly.
For Firefox 48, we’re only enabling it for classes of users that our testing shows it works well for and to begin with, we’ll only enable it for 1% of those users so we can check on the stability and engagement data and make sure nothing new and bad is showing up.
After that initial period, if all looks well, we’ll ramp up to 100% of those users, which will be about half of all Firefox 48 users.
Source What’s Next for Multi-process Firefox
When we hit release in about six weeks, not all of our Firefox 48 users will get E10S. The teams have been working really hard but we’ve still got some compatibility and other work to do to make E10S ready for everyone.
The groups that will have to wait a bit for E10S account for about half of our release users and include Windows XP users, users with screen readers, RTL users, and the largest group, extension users.
...
Add-ons
If our Beta testing goes well, in Firefox 49 we will enable the multi-process architecture for users with a small set of add-ons that are known to work well with the multi-process architecture.
In Firefox 50, again provided beta testing goes well, we plan to enable the multi-process architecture for users with add-ons that have either set a flag to say they are compatible or that were built with our new WebExtensions add-on API which is compatible by design.
Eventually we will enable the multi-process architecture for all users and add-ons that are incompatible may no longer work. For this reason it is imperative that add-on authors update their add-ons to be compatible with the multi-process architecture.
