According to this blog post, you need to set -moz-appearance:textfield; on the input.
input[type=number]::-webkit-outer-spin-button,
input[type=number]::-webkit-inner-spin-button {
-webkit-appearance: none;
margin: 0;
}
input[type=number] {
-moz-appearance:textfield;
}<input type="number" step="0.01"/>