Maybe you didn't notice, but these guys are fighting with each other. Read the story here.
In related news, IBM encourages now its employees to use Firefox. That's good news for my favourite piece of software. How is this related to Google and Microsoft? Well, Firefox is erroding Internet Explorer's market share. Since IE is the de facto standard in browsers, Microsoft controls what technologies people use when accessing the web. This way Microsoft can trump Google when they try to introduce more and more web applications to the public. So the interest of Google would be (IMHO) is to have more browsers competing and web standards defined by a third party like W3C. And Google already hires two main Firefox developers.