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;