Edwin's statement

via Tim Reynolds:

This morning I offered my resignation to Larry Beinfest and the Marlins, and they accepted. I am grateful for the opportunity the Marlins gave me to manage at this level. It was a very hard decision for me to make, with the positive way the organization is moving; a new ballpark next season and the young core of players that this team has. I can’t say enough about the effort that this staff and these players have put into this season. I could tell that they continued to give 100% effort each and every day on the field. I wish this organization, staff and players nothing but success in their futures.

This only strengthens my assumption that Edwin asked (or was asked) to resign as an alternative to being fired. He offers no reason, not even the "spend more time with my family" facade.