I think there is a difference, from which table to which other table the relation goes. I will rewrite your queries, as I believe they will be interpreted (and therefore, as I believe they should be formatted, to make the meaning clear):

SELECT *;
  FROM a ;
    JOIN b ON a.f1 = b.f1 ;
    JOIN c ON b.f1 = c.f1

Table a is joined with b.
Table a is joined with c. Therefore, the part "on b.f1 = c.f1" is not appropriate.

SELECT *;
  FROM a ;
    JOIN b ;
      JOIN c ON b.f1 = c.f1 ;
    ON a.f1 = b.f1

Table a is joined with b.
Table b is joined with c.