Good Luck Rated 2 out of 5 stars
This may be the single most important add on for firefox after firebug.
Only that it is not ready yet, it totally broke my css.
What I would love to see is a merge of this and firediff (https://addons.mozilla.org/en-US/firefox/addon/firediff/) - firediff is great because it track specific line changes to your css and gives you a diff format output, the only thing it misses is the apply button which this add-ons perfectly provides.
I don't know how realistic is that but what I'm saying is don't try to reformat the whole style sheet and just apply the changes to the changed lines.
Good luck anyway.