You can essentially do this with a userstyle (CSS).
Proof of concept:
.innerOP {
display: inline-block !important;
max-width: 20% !important;
}
.textBrowserBreaks {
display: none !important;
}
.divPosts {
display: inline-block !important;
max-width: 78% !important;
}
.postCell {
display: inline-block !important;
max-width: 20% !important;
vertical-align: text-top !important;
}