I found that using -moz-
prefix for calc
function leaves it untouched after minifier.
Example:
.some_class {
width: calc(24.3% - 30px);
width: -webkit-calc(24.3% - 30px);
width: -moz-calc(24.3% - 30px);
}
Becomes:
.some_class{width:calc(24.3%- 30px);width:-webkit-calc(24.3% - 30px);width:-moz-calc(24.3% - 30px)}