Background: I need to run an enterprise web app on selected PCs and Macs, the browser will not be used for browsing, do not highlight security risks. I must absolutely use Firefox 48 because it is the latest version to support showModalDialog() I installed Firefox 48 on Windows and everything is ok, it works as it should. On MacOS Sequoia, on the other hand, Firefox starts, the menus in the “Apple” bar at the top are usable, but the browser window is totally transparent, only the border and title bar are slightly visible. I read on the support forum that it might be enough to disable hardware acceleration, but I can't do that because the options page doesn't even show!