CSS (Keyframes): Sorry, the at-rule @-moz-keyframes is not implemented

Question

While validating for CSS3, following error can be seen for my Website:

Sorry, the at-rule @-moz-keyframes is not implemented

Below is the CSS code:

Line 16:

@-moz-keyframes spin {
    0% {
        -moz-transform:rotate(0deg)
    }
    100% {
        -moz-transform:rotate(359deg)
    }
}
@-webkit-keyframes spin {
    0% {
        -webkit-transform:rotate(0deg)
    }
    100% {
        -webkit-transform:rotate(359deg)
    }
}
@-ms-keyframes spin {
    0% {
        -ms-transform:rotate(0deg)
    }
    100% {
        -ms-transform:rotate(359deg)
    }
}
@keyframes spin {
    0% {
        transform:rotate(0deg)
    }
    100% {
        transform:rotate(359deg)
    }
}
.fa-rotate-90 {
    filter:progid:DXImageTransform.Microsoft.BasicImage(rotation=1);
    -webkit-transform:rotate(90deg);
    -moz-transform:rotate(90deg);
    -ms-transform:rotate(90deg);
    transform:rotate(90deg)
}

I would like to know what kind of CSS validation Error is this and what can be the better solution for this error

Answer 1

According to caniuse , the -moz-animation (and corresponding @-moz-keyframes ) was used by Firefox 5-15.

Most likely the validator you're using assumes (rightly) that effectively all serious users (at least 99.65% of Firefox users , even less in the total scope of things) will be using a more modern Firefox than Firefox 15.

As a result, it's pretty safe to leave it out if you're want to remove the "error".