Styling placeholder on Firefox

Question

What I want to do is to make a placeholder appear on the center 50% top and 50% left. It appears to be good in Chrome but not on Firefox 23. I have an example here.

Answer 1

I tried some weird stuff, but that seems to fit :
See this jsFiddle

You will have to put the required attribute on you textarea :

Here is the CSS :

textarea {
    height: 300px;
    width: 300px;
    /* center the text by default */
    text-align:center;
    resize: none;
}

/* align the text left when insert */
textarea:focus {text-align: left;} 
/* textarea not empty will have text align left */
textarea:not(:invalid) {text-align: left;}
/* remove the red shadow of firefox if textarea is empty */
textarea:invalid {box-shadow: none;}
/* hide the placeholder on focus */
textarea:focus::-moz-placeholder {opacity: 0;}

textarea::-moz-placeholder {
    position: relative;
    font-size: 16px;
    font-style: italic;
    color: #ABABAB;
    /* the main trick to center the placeholder vertically */
    line-height:300px;
}

textarea::-webkit-input-placeholder {
    position: relative;
    font-size: 16px;
    font-style: italic;
    color: #ABABAB;    
    line-height: 300px; 
    /* keep the placeholder centered under chrome */
    text-align: center;
}