Web Inspector is lacking Fullscreen-mode. This can be especially a great feature while debugging remotely or on a second screen. "Enabling a window of your app to assume full-screen mode, taking over the entire screen, provides users with a more immersive, cinematic experience. Full-screen appearance can be striking and can make your app stand out. From a practical standpoint, full-screen mode presents a better view of users’ data, enabling them to concentrate fully on their content without the distractions of other apps or the desktop." –– "Implementing the Full-Screen Experience" [1] [1] https://developer.apple.com/library/mac/documentation/General/Conceptual/MOSXAppProgrammingGuide/FullScreenApp/FullScreenApp.html
*** This bug has been marked as a duplicate of bug 123510 ***