Created attachment 311971 [details] Two screenshots about the bug Since I'm using WebKit instead of Safari, Facebook website looks crazy: left column is forced to left side os window, and right column changes to left side if I go down since the end of that column. This doesn't happen in Safari 10.
<rdar://problem/32602898>
This is a behavior change after https://trac.webkit.org/changeset/217522/ but the page is doing weird stuff for Safari only; it's fine with Chrome user agent.