Well, "to believe in sth blindly" means to believe in something without questionning it, but then it also has a pretty strong negative connotation, as it pretty much means the person in question has no critical approach at all. I've never heard someone say that out about his/her own belief, as it usually means the belief is in fact unfounded. This explains why I decided to consider it as not quite right.
"a mort" ( literally "to death" ) basically just means "a great lot". Since it's an informal expression, I personally would have translated it to "I totally believe in it" or (a little less idiomatic) "I really believe in it".
Thank you Coco, I edited it with "totally". Actually, I didn't know that "to believe blindly"
had only a negative meaning in English. In Italian "credere ciecamente" may be also positive, when it means to have complete confidence in someone/thing