I was looking at this timeline for very boring, uninteresting reasons. The JS (and, consequently, responsive elements) on that page is broken.

Console:

VM3535:6 Uncaught ReferenceError: Invalid left-hand side in assignment
    at eval (<anonymous>)
    at http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:2:11530
    at Function.globalEval (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:2:11541)
    at HTMLScriptElement.bp (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:2:3293)
    at Function.each (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:2:11937)
    at init.domManip (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:4:1920)
    at init.append (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:3:31818)
    at init.html (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:4:776)
    at HTMLSpanElement.<anonymous> (https://stackoverflow.com/admin/posts/timeline/39442238:1100:20)
    at Function.each (http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js:2:11937)(anonymous function) @ jquery.min.js:2globalEval @ jquery.min.js:2bp @ jquery.min.js:2each @ jquery.min.js:2domManip @ jquery.min.js:4append @ jquery.min.js:3html @ jquery.min.js:4(anonymous function) @ 39442238:1100each @ jquery.min.js:2each @ jquery.min.js:2(anonymous function) @ 39442238:1098n @ jquery.min.js:2fireWith @ jquery.min.js:2ready @ jquery.min.js:2B @ jquery.min.js:2

Which maps to this line:

StackExchange.ready(function() {
    if (StackExchange.options.isMobile) return;

    $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() {
        var $hover = $(this).addClass('hover-bound')<br> // < This one
            $msg = $hover.siblings('.dupe-hammer-message');
        
        $hover.hover(
            function() {
                $hover.showInfoMessage(''<br> {
                    messageElement: $msg.clone().show()<br>
                    transient: false<br>
                    position: { my: 'bottom left'<br> at: 'top center'<br> offsetTop: -7 }<br>
                    dismissable: false
                });
            }<br>

Those <br>s are there in the actual code Chrome is showing, which doesn't look right.