Looks great. Quick bug report - when working on an actual invoice I ran into issues on FireFox ESR 24. (I would imagine this happens any time a user restricts access to rendering PDFs on screen or in the browser as objects?) It pops up the "Open or Save" dialog each time a change is made and the object fails to load in the window below. Perhaps detecting the issue up front and then offering a "download" button when complete would be an alternative.
