If you’ve enabled Electrolysis aka e10s or Mozilla done that for Firefox Nightly on your computer, have you spotted that? If you use Screen Capture software like Snagit, you’ll notice e10s disabled in Firefox browser and browser settings under startup shows this entry grayed out: Enable E10S (multi-process) (disabled: An accessibility tool is active).

Enable e10s option grayed out in Settings

You can’t re-enable e10s again in the browser, let us see how to fix this.

UPDATE: Force-enable both E10s and Accessibility Support in Firefox Nightly

Mozilla adds ‘Enable E10s’ Option to Nightly Preferences

Re-enabling disabled E10s due to accessibility tool

1.Visit about:config

2. Search for ‘a11y’ (without quotes) in the filter, select preference browser.tabs.remote.autostart.disabled-because-using-a11y and toggle its value to ‘false’.

3. Restart the browser, now multi-process feature for Firefox will be enabled.