User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0 Build ID: 20160105164030 Steps to reproduce: I selected Firefox's "Show my windows and tabs from last time" option, and then closed (exited from) the browser. Then, I re-opened Firefox. Actual results: The windows and tabs all loaded correctly, but the windows loaded in a seemingly random order. By "order", I mean the order they appeared on my (Windows) Taskbar. The first window occupied the first spot in the Taskbar, but after that, I couldn't tell why certain windows appeared in certain spots. Expected results: The windows should have loaded (or shown) in the same positions they occupied at the moment that I exited Firefox.

Previously, I had experienced the bug in [Bug 712763] in Firefox 40, but then when I upgraded to Firefox 41, I seemed to no longer have the issue. But, then after upgrading to Firefox 42, I encountered this bug, which differs in that the windows restore in a random order rather than a reverse order.