Re: Why bother?
Essentially, because the browser is also the runtime.
Now I don't agree with the assertion that the browser should always be the entire development environment, but you certainly need development tools in it. The reason for that is because the browser also runs the client side code, so the only way to debug the code is inside the browser. Therefore you need a debugger inside the browser, or you need to have the ability to run the browser's Javascript engine outside of the browser in such a way that you can debug it using the IDE of your choice.
Anyway - it's kind of a moot point. Modern browsers have development tools built in, and the vast majority of users have absolutely no idea that they're there since you typically need to actively do something to access the tools.
