If you have 300 columns as you mentioned in another comment, and you want to compare on all columns (assuming the columns are all the same name), you can use a NATURAL LEFT JOIN
to implicitly join on all matching column names between the two tables so that you don't have to tediously type out all join conditions manually:
SELECT a.*
FROM tbl_1 a
NATURAL LEFT JOIN tbl_2 b
WHERE b.FirstName IS NULL