If the Day of 'Arafah falls on a Friday, is it obligatory to fast the day before it or not?

There is no objection to singling out Friday for fasting if it coincides with the Day of 'Arafah, for the prohibition of singling out Friday for fasting is specific to those who intend to do so, and it is a prohibitive 'tanzih' (discouraged) rather than a 'tahrim' (forbidden) prohibition. It is preferable to fast all nine days of Dhul-Hijjah for those who are able.