And on my Chrome, there is a regular inconsistent bug that when I want to inspect an element, the new tool UI is displayed but the element is not selected.
My point though is that it's first in recent years that we've had tools like these, and they made a huge difference for me helping me undesrtand what the hell goes on with the styles. It's a much nicer workflow than the old edit-reload-check-edit-reload-check model, where you inserted coloured borders to see exactly how large your divs were, and moved things a few pixels at a time until it looked right.
For simple CSS you probably want to be changing it in a seperate text editor that auto-refreshes your web-browser so you have the benefit of being able to save.
The CSS-changing feature you mentioned is of questionable use while the JavaScript features are essential.
I switched to Webkit's JS debugging tool not long ago, it has much better warnings than Firebug.
Usually, I draw a basic sketch on a piece of paper, then write the HTML file in TextMate, and then spend a lot of time in CSSEdit.