I am developing websites using Visual Studio 2017 on a Windows 10 guest OS and am experiencing an annoying display artefact when using the developer tools in both Firefox and Edge. Chrome seems to be OK. If I choose Inspect Element to open the Developer Tools window for either Edge or Firefox then hover over different elements in the Inspector tab, the element under the cursor is highlighted but the rest of the web page goes black, making it very hard to see what is going on. This behaviour is consistent at the moment despite rebooting the OS and Parallels itself. Any ideas?