Is this for mingw Firefox build? I've been meaning to submit header patches for it. I also had a patch to add IDispatcherQueue for graphics capture, windows.ui.composition.idl too. It looks like Firefox also needs windows.ui.core which I have here: https://gitlab.winehq.org/maljaf/wine/-/commit/4d4f46507dee8eef096b15f974b26...
I'll have to split them up for easier review, they're fairly large.
Also, you're adding definitions here, not declarations.