Ok so there are 4 things we need to deal with in order to achieve the goal of a newer Gecko on Fremantle.
First is dealing with things that newer Gecko needs that Fremantle doesn't provide (i.e. kernel changes, GTK stuff etc) and figuring out how to work around those (or how to bring them into Fremantle)
Second is dealing with Maemo/Fremantle specific functionality and changes (e.g. the stuff that deals with network connectivity via various Maemo libraries or e.g. various dialogs and bits present in microb-engine) and identifying all the things that were removed but need to be brought back.
Third is dealing with ABI incompatibilities between old plugins and newer Gecko (with the exception of Flash and maybe Maps, we can probably clone all the plugins if we need to)
And last is dealing with the external interface used by other things (browser ui, maps, messaging etc) to talk to the browser and making sure we are ABI compatible with that interface.