Tested with reactos-bootcd-0.4.14-dev-1185-g3ecbbd9-x86-gcc-lin-dbg.iso
I noticed this bug when I tried out the 2D CAD web application I'm developing in my daily job. I can't give access to it, since it's internally used, but the same bug can be observed visiting this w3c sample page:
When hovering the mouse over the "url" word a red ball should appear, but it's not working.
The important line from the debug log is this:
Firefox calls CreateDIBitmap with BI_BITFIELDS compression when a custom cursor is in use, so this compression should be valid.