I was instantly excited. This is a feature I’ve always wished for but couldn’t find in firebug – saving your changes while messing with things in the dev tools.
I’ve always found it so annoying when I’m tweaking some css and I get to the point where it’s perfect – but I can’t remember all the things I changed. For that I’ve always wished I could save the current css and do a diff against the original. With the diff I could be sure that I hadn’t forgotten to nudge a div a bit this way or changed the color of an element.
In Chrome’s implementation, they take it one further by saving multiple versions. I can see this being very useful when I want to click back and forth and compare different sets of changes.
I find it hard to believe this isn’t in Firebug or a firebug extension. It does seem to be a popular request.