User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20170712030204 Steps to reproduce: Create new profile. Open Firefox [56.0a1 (2017-07-12) (64 bits)] (on Windows in my case). Go to customize. Select Theme:"Bright Compact" with Density:"Compact". Maximize windows. Actual results: There are no buttons on the right of the title bar. They are still clickable and have the expected effect (minimizing, maximizing, closing). They reappear when un-maximizing and when closing (before the window disappears). They are visible when the window is not maximized. Expected results: The buttons should stay visible even when windows is maximized.