> Also, the move to WebExtensions is a move to a more secure extension model. Traditional XUL extensions were comparable to the extension developer compiling their own code into the browser. Yikes.

Not if you previously moved to the Jetpack, err addon-sdk with cfx, err jpm tool. Now there's yet-another API to move to. At least this one will make it easier to develop portable extensions (but still not straight-forward).