I'd like to edit the default bookmarks in Firefox from a bzr branch. Getting the branch seems easy. However, it looks like it is necessary to find the original file, patch it, modify it, and then make a new diff.

bzr branch lp:firefox
At that point I am stuck because the file ./firefox/debian/patches/ubuntu-bookmarks.patch is simply a patch to some other file unfamiliar to me. What are the steps needed to get the source, patch it, (edit it), and then make a new diff?