Inserting CSS with a Firefox Extension

Question

Hi

I'm building a Firefox extension that adds HTML elements to certain pages of a website. I want to have it insert a custom CSS file to style those elements. It works if I insert tags with the CSS right on the page, but that's a less than ideal solution.

Is there anyway to get it to load and parse a CSS file, as if I used the tag in the header, or am I stuck inlining it somehow?