Checking over that code and going by the "last updated" dates, the only source code we now have that we didn't have before is the proper actual PR1.3 source code for tablet-browser-daemon (and not my reverse engineered clone) and the actual PR1.3 source code for browser-neteal (including the correct not-reverse-engineered browser-neteal-dev package)

This is still VERY good though for anyone wanting to replace the browser daemon and all the libraries it pulls in or to change/extend the dbus interface between the browser daemon and the UI layer. And its VERY good for anyone wanting to use the browser in their app by talking to the browser daemon instead of loading the browser directly.

The interesting stuff in the UI layer (tablet-browser-ui, tablet-browser-view, tablet-browser-widgets, tablet-browser-controls, tablet-browser-dialogs and others) is still closed source

In terms of actually replacing the engine with a newer Gecko version, the biggest issue you will face will be any API changes between PR1.3 Gecko and whatever Gecko you move to that cause any of the closed source extensions, plugins or components (e.g. nokia maps, microb-geolocation, media player plugin, flash plugin) to fail to work.