Ok after I made this post I cam across this:
Cons
There are a few drawbacks with the addon. Currently it will only scan pages you visit. It does not have the ability to scan your entire site. Sites with 100's of pages may be difficult to scan with this tool. I also found the line numbering to be a bit flaky (as seen in my screenshot above).
Pros
Some great pros of this addon include cleaning up your stylesheets and reducing filesize. You can also save a little bandwidth by making them smaller in size.
http://www.nealgrosskopf.com/tech/thread.php?pid=66
And the link to the above point to Firebug add on Here:
https://addons.mozilla.org/en-US/firefox/addon/1843
So I am off to test it out..