CSS filter grayscale not working in Firefox

Question

I'm having troubles doing a transition from grayscale to colored, it works in chrome, but that is it.

Here is the HTML:

<div id="post" style="background-image:url('bg.png');background-repeat:no-repeat;">
    <p><a href="/post.php?id=1">Title - Date</a></p>
</div>

Here is the CSS:

#post{
    padding:0;
    margin:0 auto;
    margin-bottom:25px;
    border:solid 1px #000;
    height:150px;
    width:750px;
    display:block;
    filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'saturate\' values=\'0.5\'/></filter></svg>#grayscale");
    filter: gray alpha(opacity=50);
    -webkit-filter: grayscale(50%);
    -webkit-transition: 0.3s all ease;
    -o-transition: 0.3s all ease;
    -moz-transition: 0.3s all ease;
    transition: 0.3s all ease;
    -webkit-backface-visibility: hidden;
}

#post:hover{
    filter: none;
    -webkit-filter: grayscale(0%);
}

Thanks for any help, it's appreciated.

Answer 1

Try setting #post:hover to this:

  filter:grayscale(0%); 
  -webkit-filter: grayscale(0%);
  filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'1 0 0 0 0, 0 1 0 0 0, 0 0 1 0 0, 0 0 0 1 0\'/></filter></svg>#grayscale");

You can look it up here. http://www.cheesetoast.co.uk/add-grayscale-images-hover-css-black-white/

in case tutorial link will be dead works in: Safari 6.1.1, Firefox 26.0, Chrome 32.0.1700.77

.slides li img{
  filter: grayscale(100%);
  -webkit-filter: grayscale(100%); /* For Webkit browsers */
  filter: gray; /* For IE 6 - 9 */
  -webkit-transition: all .6s ease; /* Fade to color for Chrome and Safari */
  filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale"); /* Firefox 10+, Firefox on Android */
}
.slides li img:hover{
  filter: grayscale(0%);
  -webkit-filter: grayscale(0%);
  filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'1 0 0 0 0, 0 1 0 0 0, 0 0 1 0 0, 0 0 0 1 0\'/></filter></svg>#grayscale");
}

As noted by Adam below: From Firefox 35 filter: grayscale(100%); should work.