This #ifdefs out the multiview for non-photon-theme, and checks for it being present in various bits of JS that interact with it. As a result, this will 'fix' the issues in this bug and in bug 1370967 for 55 as it moves off Nightly. bug 1370967 will still need fixing in the photonpanelmultiview / webextensions. MozReview-Commit-ID: 6x4HmyvxeRP