Don't use placeholder instead of label for form input.
<h2 class="window-title">{"Shaare a new link"|t}</h2>
<form method="GET" action="#" name="addform" class="addform">
<div>
- <input type="text" name="post" placeholder="{'URL or leave empty to post a note'|t}" class="autofocus">
+ <label for="shaare">{'URL or leave empty to post a note'|t}</label>
+ <input type="text" name="post" id="shaare" class="autofocus">
</div>
<div>
<input type="submit" value="{'Add link'|t}">