Comment 39 for bug 350407

Here's the problem that I've found, and correct me if I'm wrong because I'm not intimately familiar with the code:

At the moment, nsWebBrowserPersist.cpp uses a Tree Walker (line 1581) to go through each and every "tag set" (node) and find references to external objects. Since the CSS is not parsed in the DOM, the Tree Walker doesn't find these images and stuff. Therefore, the style sheets also need to be parsed or stuff inside import() and url() would need to be collected as well.