I tried setting up a cross-compile environment under a fully updated Ubuntu 16 LTS but had trouble when it came to looking for Microsoft headers & libraries. When you have a moment, Jens, would you mind sharing what you did for this portion of your environment? I found a thread about building VLC for Windows that provided a little info but wasn't nearly complete. And I found a ref to Wine & Windows 7 (http://www.kegel.com/wine/cl-howto-win7sdk.html) but didn't try replicating this with newer MS packages. In the long run, it was easier to just grab the mozilla build environment for Windows and build 52.0.2 from the command line with mach & Visual Studio's compiler.