Spending time working on the canvas tag has given me a much greater insight as the how XUL layout actually works. I think I know enough that I can fix layout-related bugs in XUL. Actually, I did fix one, bug 214956. I'm also now familiar with parts of gfx (the graphics code), and from earlier tasks, the RDF code. One day I should sit down and update the RDF parser so that it is not only less buggy but to support some of the newer features in the latest working draft.
With regards to the canvas stuff, it is coming along very nicely. It supports all kinds of things. I'll provide a list of what it supports once I've polished it a bit more.