Ruling on working for a Christian who makes fun of Islam

Firstly: 

It is
permissible to work for a kaafir or mushrik, so long as one does not approve
of anything of his disbelief or sins. So it is obligatory to object to him
if he makes fun of Islam or Muslims. It is also obligatory to adhere to
Islamic guidelines such as not regarding him as a friend, not being the
first one to greet, and so on. It is better to work for a Muslim who fears
Allah. 

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) was asked: There is someone who
works with the kuffaar; what advice can you give him? 

He replied: We
advise this brother who works with the kuffaar to seek work where there are
none of the enemies of Allah and His Messenger who follow a religion other
than Islam. If this is possible, then this is what he should do. If it is
not possible then there is nothing wrong with it, because he is doing his
job and they are doing theirs, but that is on condition that there be no
fondness or love or feelings of friendship towards them in his heart, and
that he adhere to the rulings of Islam concerning greeting them, returning
their greetings, and so on. Also, he should not attend their funerals or
celebrations, and he should not congratulate them on their festivals.

End quote from
Fataawa ash-Shaykh Ibn ‘Uthaymeen, 3/39 

Secondly: 

It is not
permissible to stay away from work whilst recording it as if one were
present, because that is lying. What you have to do is strive to attain your
rights in proper, legitimate ways. 

What you have
to do is render back trusts that he has entrusted to you, and fulfil the
conditions that he stipulated for you in your work with him. 

And Allah knows best.