Firefox new version 57 has an annoying white space at the top of window. Earlier, when I need to switch between tabs, I could quickly move my mouse to very top of the screen and click on the tab. Now, I have to spend extra effort to move it a few pixels down from the top of screen and click. Similarly, to close Firefox, I could quickly move mouse all way to right-top without looking , and cursor would stay on the 'X' and I could close it. The drag-space option is already unchecked. How to remove this annoying 'enhancement' and get back to old method ?