Is another browser really necessary?

Everyone seems to think that Google is going to introduce a web browser, possibly called Gbrowser. While I am sure that they would do an excellent job, I question the wisdom of yet another web browser (YAWB).

I use Firefox, and I often encounter web sites (like Weightwatcher.com that I mentioned recently), that design their sites for one browser. Others are just not able to their sites with multiple browsers, and the introduction of more browser idiosyncracies will just complicate the problem.

I understand Google’s desire to expand their grasp of the desktop, but perhaps they could do that by striking and agreement with an existing browser like Firefox or Opera, and minimize the pain for net users everywhere.