title: How can I disable one specific CSS file on a site, and replace it with a local version?
body: <p>I'm trying to re-skin an existing site using CSS only.  I will be taking one of their CSS files and redoing it to match a new design, without changing any HTML.  I want a good way of continually updating and then testing, but I have to do it locally because they do not have a dev environment.  The site itself is dynamic and authenticated, so I can't just download pages from the site and test the entire thing locally.  I was hoping that there is a way to tell my browser (Firefox, preferably) to disable that specific remote CSS file and replace it with a local file.  </p>
  
  <p>I don't want to use something like Web Develop Toolbar or Firebug because that requires me to manually make the changes each time I load a page.  I want something more seamless.</p>
  
  <p>I was thinking one possibility is to load my new stylesheet in userContent.css, but I would still need a way of telling the browser not to load the original stylesheet from the server.</p>
  
  <p>Any ideas?</p>
  
  <p><strong>UPDATE:</strong> I found this Mozilla bug report <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=208641" rel="nofollow">https://bugzilla.mozilla.org/show_bug.cgi?id=208641</a> discussing the issue of being able to change userContent.css without restarting Firefox.  One of the posters (Simon Wilper) posted some files and info about adding a menu item to refresh userContent.css, but it talks about modifying browser.xul and I can't find that file on my system.  This seems like the last piece of the puzzle.</p>