I have found the exact same question here: https://support.mozilla.org/de/questions/800063 But since the thread has been closed in the meantime, I'm opening a new one. I have the same problem as described there, my title bar goes fully transparent and the right hand icons (close, minimize, restore) are invisible / flash up when hovering over them, but are unusable. The interesting bit is that this can also happen to just one Firefox window if multiple are open, e.g. window #1 works fine, but window #2 shows the buggy behaviour. Opening new windows, and even dragging out tabs from the bugged one into a new window works just fine. I can also still double click the (transparent) header and the window goes into fullscreen/windowed mode, so the functionality itself is still there (bar the icons). I was not able to consistently repdroduce the problem, it just happens from time to time, and when it does, I cannot get the window to work correctly again (minimizing, moving to another monitor, dragging tabs into it all does not work). I _do_ have a title bar addon installed on my Firefox 17 (Aero Window Title 1.6), but as the previous thread doesn't mention it, and the problem occurs only sporadically, I'm inclined that this problem isn't necessarily related to that addon.