Do we care about browser security? I mean it's the client, the user's browser. Unless the user is you, you probably don't have a lot of control over this environment in the first place. So, who cares, right?
A couple of years ago I might have agreed. But with new web technologies and techniques such as Ajax and Flash pushing more responsibility onto the client, the browser can no longer be totally ignored.
The design contract between the user and a web page is changing. How do users know when the page is loaded if the browser's "loading" icon doesn't stop spinning? Rather than a simple request-response model, the page now can make micro requests, moving some session state to the browser. The browser is now a first-class citizen in the application's data flow, and we have to start thinking about it differently.
Each page now plays a major role in the application, and in some ways the page is the application. Therefore, we need to care more about what technologies are running out on the browser and how best to help secure that environment. Developers are forced to think more about what is happening on the client and react accordingly.
At some point it becomes important to care about the security of the browser. After all, your users are using browsers, and if your application is running code in the browser, it should be secure. You may not be able to control everything out there, but if you do even a little to help educate your users, the Internet can be a safer place. ...