Depending on where you live, you may only have to leave early on Fridays
12-16 times a year and it may only require leaving an hour or so early. So,
if you put it to your boss this way, it won't seem like a lot. Also, you
might want to arrive earlier on Fridays in Winter.
Offer to work on non-Jewish holidays. Use your personal days or vacation days.
If you feel that you lost your job due to religious discrimination, there
are many agencies that will take your case for free including your state
civil rights dept.