Rats, update failed, downloading full update (6.0MB), could be a couple of things not necessarily firefox's fault.
1. I was running firefox using dropmyrights, which may have stopped updating/install of software.
2. I also used a UPX exe compression tool, UPX125w that compresses large exe files, which speeds the loading (for me anyway) of the exe and firefox.
So next time I will have to try it without the exe compression and unrestricted running of firefox and see if the new update function works.