I'm using Firefox 55 beta (the same happened with older versions) and when I force the multiprocess setting browser.tabs.remote.force-enable to true (I suppose it is disabled by default because of addons) some pages doesn't work saying that I've the cookies disabled. Messages like this: "Cookies are disabled. Cannot access mid-tier with this setting. Please configure your browser to accept cookies." I tried to start in safe-mode (without addons) but the same happens. With Firefox Nightly (not needed to set browser.tabs.remote.force-enable) it works. Ideas?