possible bug or misunderstanding

I received the following errors

17	.main	Property -moz-border-radius doesn't exist : 25px
20	.main	Parse Error opacity=75)

while validating the following code as CSS3:

..main
{
	width: 960px;
	height: 672px;
	padding: 8px;
	border-radius: 25px;
	-moz-border-radius: 25px; /*Firefox 3.6 and earlier*/
	background-color: #ECECEC;
	opacity: 0.75;
	filter: alpha(opacity=75); /*For IE8 and earlier*/
}

But, these lines are suggested in the w3 tutorials. See, for example, http://www.w3schools.com/css3/css3_borders.asp

div
{
border:2px solid;
border-radius:25px;
-moz-border-radius:25px; /* Firefox 3.6 and earlier */
}

or http://www.w3schools.com/cssref/tryit.asp?filename=trycss3_opacity

<style type="text/css"> 
div
{
background-color:red;
opacity:0.5;
filter:Alpha(opacity=50); /* IE8 and earlier */
}
</style>

I am not looking for free advice on how to code; but I don't understand if I am committing an error or if the validator is not validating correctly. Please elucidate to whatever degree you think is appropriate. Thank you very much.

ronald b. kopelman