For the time being I have also disabled e10s because it does not yet, and I suspect never will, support userContent.css and userChrome.css.<p><a href="https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1046166" rel="nofollow">https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1046166</a><p>Eventually, I will need to migrate my user styles to a plugin such as Stylish, but I have preferred the minimalism of userContent.css.<p>However, seeing the mention of a multi-process user interface elsewhere in this thread is tempting me to ditch userContent so I can re-enable e10s with the multi-process UI, at least once the kinks are worked out.