Please use it in the field attribute Title.
ie
original text This is my long field name
Title text This is <br /> my long <br /> field name
displays as
This is
my long
field name
RE: qListform: Adjust field label size
Please use it in the field attribute Title.
ie
original text This is my long field name
Title text This is <br /> my long <br /> field name
displays as
This is
my long
field name