Recently, Mozilla pushed a notification to Nightly users to test e10s, if you’ve not enabled and tested it then, Mozilla has now enabled electrolysis by default with an update to Nightly build. After installing the latest update, you can see multi-process feature enabled in the browser with an info bar on top saying ‘You’re now helping to test process Separation (e10s)! please report problems you find.’
Disabling e10s in Firefox
There are issues currently with this feature, and Nightly may not work with some websites and add-ons, you can disable e10s by visiting ‘Options’ page and unticking ‘Enable E10S (multi-process)’ under ‘Startup’, you need to restart your browser for the changes to take place. You can check all known and add-on compatibility issues with e10s here.
Note: You can also disable e10s by turning browser.tabs.remote.autostart preference value in about:config to ‘false’.
After restart, input.mozilla.org tab opens for you to submit your experience. Check your favorite add-ons working or not with e10s on the page http://arewee10syet.com.