Hi! I have the same problem here. I develop a lot of OpenGL applications, and lately I've noticed that whenever I have Mozilla Firefox (3.6.4) opened, my OpenGL application fail to become 100% fullscreen as they should. Here is what it happens: first I execute the application, after a few seconds of flickering the window appears, but the taskbar is in front of the window and moreover the window of my OpenGL application is not focused, i.e. it won't receive any mouse or keyboard input. Even though I create this window with WS_POPUP and WS_EX_TOPMOST flags, and I properly change the resolution with ChangeDisplaySettings( &dmScrSettings, CDS_FULLSCREEN ). And I have to click once inside the window to make it 100% fullscreen and focused, BUT this doesn't work always. But if I close Firefox and try to execute the application again, everything works just fine, the OpenGL windows is now 100% fullscreen, topmost and focused. I don't know if this is related to Windows 7 ( i have Windows 7 Ultimate x64) or to this version of Mozilla Firefox, but i didn't have this issue while programming in XP or Vista. I also can confirm that it's not because my code, because I've test this issue with plenty other OpenGL samples downloaded from the internet, and the problem persists. I hope someone will fix this, thanks in advance! - Mike