Firefox and Chrome now work together via WebRTC. To prove it the development teams had a chat using nothing but their browsers and without a server or a plugin to be seen.
Well, yes, it is true that standards are supposed to work together and so you might think that this is news of the obvious. However, WebRTC is currently a matter of some controversy. Microsoft thinks that it is basically not up to the job and has proposed and implemented its own API for browsers to show what it means. The WebRTC committee isn't impressed and wants to continue developing the standard as it is.
Seen in this light the fact that Firefox talked to Chrome has to be seen as much a politcal statement as a technological achievement. Given that WebRTC is a complex API, the fact that both browsers have implemented it in a compatible way is an achievment. The WebRTCPeerConnection was used to establish a two-way audio and video link betwen the two browsers.
You can see the "historic" moment in the video:
Of course, IE didn't turn up for the party and the fact that Mozilla and Google are working together just isolates IE and Microsoft even futher. The big problem is that WebRTC is a possible threat to Skype, which Microsoft recently acquired and is currently busy integrating into its products.
WebRTC is an exciting technology and if you can't think of ways to use it then you probably aren't thinking about it. Creating audio and video links between browsers is just the start of the process.