Mozilla, for a year or so, has been working on a complete set of tools for developers, built into Firefox. The reason is obvious, keep developers happy and they're more likely to create websites and apps with your browser in mind.
Google is not lagging behind either, the Web Inspector set of tools is still more complete, albeit less snazzy, than the Firefox equivalent.
The latest small additions
may seem insignificant, but it's this type of things that add up in time. For example, the Web Inspector now supports filtering in the Network panel.
What this means is that it's going to be easier to focus on the stuff that you're interested in and filter out the rest. It's an obvious addition, but it's a useful one.
Another new option is the ability to switch to the BlackBerry 10 user-agent, for debugging purposes. Finally, in an effort to bolster performance, changes are being done to have the panels load independently and in a delayed fashion, first loading the visible one, then the other ones when appropriate. Note that all of these changes are only available in the latest Chromium 23 builds.