What should I do if an investment firm accidentally puts $ 1M (million) into my bank account? Is it ok to spend it ? or i should contact them ?

You Should Contact With Them

don't waste your time here, just withdraw the amount and evaporate......

 

jokes apart..... you should contact them immediately..... 

Contact firm and help them to withdraw their amount from account which has wrongly hit the account

You should keep in mind that your account might be hacked and used for money laundry. So before you get excited with the money you should worry about the FBI whom are going to hunt you down. Eventually the money has to be reported officially, so when they come to your door your defence is officially ready. Hope you understand the risk of founding a big number hitting your account for no reasons.

Any amount big or small it is not my right

And it did not tired

 

I'm going to repeat it without thinking and

Depends on your honesty and your image.