After messing for one hour against code wondering why my computer was refusing to show the 'share calendar' icon, I finally found out that it was Firefox and Chrome ABP plugins who were silently hiding it. In fact I only realised about the existence of the icon after using a friend's computer who had not installed this ad blocker. (Oh! What's that? Why don't I have it? :-D)
Additionally I found that uBlock doesn't have this effect. Hi
Adding your owncloud site to ABP exceptions will fix part of the problem, but only on the user's side. Uninformed users won't be able to share.
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