Load additional CSS file through browser add on?

Is there a way (eg a firefox add on) that lets you load a CSS file on your hard drive to a site your viewing? Im looking for something similar to firebug but where I can make more complicated changes and refresh the page to see them in action.

Than开发者_StackOverflowks

You might find https://addons.mozilla.org/en-US/firefox/addon/stylish/ to be helpful. I think was designed more for end users who want to customize the way certain sites look, not for web developers/designers. But I don't see why it couldn't be used that way.

I use this.

https://addons.mozilla.org/en-US/firefox/addon/web-developer/

very useful, and includes the feature you're asking for and also allows you to edit the css live.