User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:39.0) Gecko/20100101 Firefox/39.0 Build ID: 20150417004243 Steps to reproduce: Issue occurs whenever the Firefox window is maximised. (Currently using Firefox Developer Edition 39.0a2 [2015-04-17] and Windows 10 Technical Preview Build 10049 -- although this issue has persisted across multiple builds of Firefox Developer Edition AND Windows 10 Technical Preview.) Actual results: The content of the Firefox window "overscans" by around 4px on all sides when the browser is maximised (i.e., the outermost 4px appears to be "cut off" or "cropped" on all sides; see attached screenshot). This is particularly noticeable if you look at the tab bar (the light blue line on highlighted tabs is cut off), the scroll bars, the leftmost item on the bookmarks toolbar (in this case the Whatsapp icon), and the URL tooltip in the lower left of the screen. Expected results: Entire content should still appear in maximised windows, without any "overscan" effect.

Did you experienced this "overscanning" issue with the previous versions of Windows or when using other browsers?

Does this still happen with current Nightly and current Windows 10? If so, can you post the contents of the "Graphics" section of about:support (Help > Troubleshooting Information) and the screen size on which this happens? Also, do you use multiple screens, and if so, is this the main screen or a secondary screen and/or does it happen on all screens? Does it happen to any other applications?