[Jellby]

On the other hand, this may work in ADE, but "inline-block" and "position" are not required properties in ePub 2.0.1 (and it requires two additional spans):

<div><span class="hang"><span><span>"</span></span></span>Testing line</div>
<div>secondline</div>
<div>third line</div>

span.hang {
    display: inline-block;
    width: 0;
}
span.hang span {
    display: inline-block;
    position: relative;
    right: 0;
}
span.hang span span {
    margin-left: -100%;
}