User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:48.0) Gecko/20100101 Firefox/48.0 Build ID: 20160307063917 Steps to reproduce: 1. Start Nightly 2. Open DevTools > Memory 3. Switch view to "Dominators" (or "Aggregate", Dominators is easy for reproduce) 4. Hide heap-view-item by resizing graph pane Actual results: Horizontal scrollbar does not appear quickly if heap-tree-item is hidden. To display it, need to hide more. Expected results: Horizontal scrollbar appears quickly without hide more.

> 1. Start Nightly > 2. Open DevTools > Memory > 3. Switch view to "Dominators" (or "Aggregate", Dominators is easy for > reproduce) + Take snapshot > 4. Hide heap-view-item by resizing graph pane

Hi, magicp! I'm not sure I understand this bug report, can you highlight what I should be looking for in the screenshot or maybe attach a video or something? Is it that you expect the scrollbar to exist at a certain width, but have to make the width even smaller before the scrollbar exists?

Hi Nick, In case of attached image file, horizontal scrollbar should be appeared, because heap-tree-item is already percially hidden. I have uploaded a video. If you have any questions, please let me know.

Thanks!