First turn off all your add-ons or create a new profile.
To enable or disable multi-process Firefox, do the following
Type about:config in the browser’s address bar.
Confirm that you will be careful.
Search for browser.tabs.remote.autostart.
Double-click on the preference.
http://www.ghacks.net/2016/07/22/multi-process-firefox/
To check if your add-ons are compatible.
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