1. If there's not a share url yet (i.e. you haven't turned sharing on) then many of the options in the share tab are disabled. 2. The "Filtering is disabled" messaging is confusing -- we should probably change that to something like "no filters selected".
I should also note that if you expand the controls in the bottom of the "Display" tab, the filtering options are also there (and can be used before you turn on the share). So there's a little bug/inconsistency here as well.
If this isn't working, can you let me know what browser / OS you're using.