This is not correct - like the person you're responding to, you're mixing up security features. For one, Chrome predates Windows 8, where this mitigation was introduced, so it can't have supported it before it existed.
I think you're confusing the general "sandbox that restricts access to the kernel" with the specific mitigation here. Firefox also had the generic kernel mitigations long ago: https://news.ycombinator.com/item?id=31362935
But it's true Chrome had them first. The same thread points out that Firefox reuses Chrome's sandbox, so like in the first sentence, there are causality constraints that would make it hard for Firefox to support it before Chrome did :-)
I think you're confusing the general "sandbox that restricts access to the kernel" with the specific mitigation here. Firefox also had the generic kernel mitigations long ago: https://news.ycombinator.com/item?id=31362935
But it's true Chrome had them first. The same thread points out that Firefox reuses Chrome's sandbox, so like in the first sentence, there are causality constraints that would make it hard for Firefox to support it before Chrome did :-)