When you have the following setup: * 4K monitor with 3840x2160 resolution * 1080p monitor with 1080x1920 resolution in portrait mode * Firefox 57 is currently loaded on the 1080p portrait monitor What happens is, all the extensions you have installed use the 4K monitor's resolution instead of the 1080p monitor, resulting in LARGE TEXT, and the extension menu cannot be accessed because icons are now off the extension menu's area. Please have Firefox 57 pull the resolution info from the ACTIVE monitor where Firefox.exe is, not the MAIN monitor. In my case, the 4K monitor is number one in Windows 10. Feel free to change the Component in this bug if it's wrong. And fix this resolution error.