One could argue, especially considering some of the disclosure situations surrounding Project Zero that have occurred, that it exists more to shame competitors than improve the world. :) To my knowledge, only like once have I heard the words "Project Zero" in relation to a flaw in Google software.

But as Google definitely does do security testing on competitors' products such as Windows, it definitely goes to show that Google would be more than happy to test for security flaws in Firefox. And regardless of Google's motives, finding security flaws does, in the end, make a more secure Internet for everybody.