I upgraded my ubuntu install to 13.04 and for some reason when trying to add my facebook account to online accounts i got this:
SECURITY WARNING: Please treat the URL above as you would your password and do not share it with anyone.
here is a quick fix on my ubunto 13.04 64 bit
sudo gedit /usr/share/accounts/providers/facebook.provider
Put this under line 13,
<setting name="AllowedSchemes" type="as">['https','http']</setting>