The vulnerability is in Windows 10. Windows 10 has been fixed. It's not clear in the article what other mitigations are in place in Firefox to make exploitation more difficult.
Basically my PoC works exactly the same from Chrome GPU as FF Content Level 5 [1] there was no additional hardening. It was also easier to test as FF doesn't enable the Microsoft DLL signing mitigation should I could just do a direct CreateRemoteThread -> LoadLibrary without messing with KnownDlls.
[1] https://wiki.mozilla.org/Security/Sandbox