1. Most people use browsers compared to working with them for development, and
2. The additional tools just add to the package size and possibly increased resource usage (if they are running with the rest of the browser)?
Thanks in advance for the replies.
Once you start getting into complex frameworks and what have you, you start needing additional tooling, more knowledge, etc, but that's fine. The point is to start tinkering, you only need a browser. To start doing a little more than tinkering, you need a browser and a text editor (not like Sublime, like Notepad; on day 0 you don't care that much about syntax highlighting). Both of these come out-of-the-box on any computer.
Download size is affected, although for larger parts of the developer tools (things like firefox OS simulators and adb) we use addons. We think that tradeoff is worth the benefits - users can look under the hood (even if most of them won't), developers have quick and easy access to tools, and we don't have to worry about things like version mismatch/testing concerns/etc.
The web is not like other platforms where there's a hard line between people who make it and people who use it. Many people, like myself, thought of themselves as users until the web's view source made it possible for us to become content producers with no significant additional tooling.
Today, the Web is a lot more complex a platform than it was in the early 90s and so our view source and JS consoles have evolved into more capable developer tools as a result.
So in short you get a better, more extensible browser, more stability and the chance to take a look at how something you use every day works.
It's a win-win in my opinion.
The question is, do you want this state of affairs to be built into the design of our systems, or do you think that it would be good if, over time, a greater proportion of people are able to express themselves through code?
That was 2004 though. Today the Web is a lot more capable because browsers are a lot more capable. Also, typical download bandwidth for consumers is a lot more capable than it was in 2004.
Most of the growth in Firefox download size since then is a result of Gecko/Web platform feature growth, not the GUI features that users interact with.
That web platform capability isn't free. It takes code to make JS dozens of times faster than it was in 2004. It takes code to add HTML5 and CSS 3 features, WebGL, WebRTC, and all of the other great stuff the Web platform includes today. That code makes the download larger.
That being said, I'd love to see another round of evaluation to see what can be trimmed or slimmed. I don't consider that the same priority it was in 2004 though.
This should be a plugin like firebug.