We just had another user post about an issue of modules/buttons not showing. This looks to be a Facebook problem.. Specifically, a bug entered today looks just like your problem (I'm seeing the same Javascript errors being reported from your page):
developers.facebook.com/bugs/349984988390147
If you are seeing the missing button or other similar issues (right now, outside of your original 404 problem), feel free to click the "Does this repro describe your issue" link in the bug report.
Usually, bugs like this are fixed pretty quickly since they tend to affect many sites.. but that's not always the case. Hopefully, it's resolved soon, but definitely keep us posted if it persists.
Thanks,
Alex
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