Summary: Firefox44 bug with multi monitor and view detection, when menus rearranged for view showing on the main display while Firefox may be on another. And Firefox44 bug with layout.css.devPixelsPerPx which detects wrong view edges on scaling. Firefox 44.0 stable, Windows 7x64, two-monitor configuration (both 1920x1200). Main monitor is left, secondary is right. When Firefox is on secondary monitor maximized it shows main menu on primary monitor instead. It happens in non-maximized state too when the menu button is close to right side of the screen. When it has a distance to the right side of desktop - it shows normally. Even tooltips and context menu shows at the main monitor if the pointer was too close to right edge of the second. All of it just not so obvious as the main menu in maximized mode. If I set right monitor as primary - there is no such effect. I tried to disable all the extensions and setting hardware acceleration option on and off. Problem remains. Firefox is quite untested in multimonitor configurations I presume. Upd: installed Firefox 44.0 portable to test a fresh install and it's a bit different. Bug still occurs but only when menu button is really on right edge of desktop. In maximized window it's not and all working normal. Why my main Firefox version sees right edge too early? Problem with multi monitor menu reposition still a problem. Upd2: problem was with about:config option - layout.css.devPixelsPerPx which I used to scale Firefox UI and pages to be a little bigger. At least at 1.1 it's doing that bug with wrong desktop edge detecting. But only with multimonitor configuration with secondary display right from main it really emerge so ugly. How to report that?