See here for a detailed changelog.
N78 v20.149 update is real
Published by Steve Litchfield at
Despite some glitches at Nokia's end, telling me the N78 was already up to date and that the firmware version available was the same as the current one, v12 - hey, I 'updated anyway'. And lo and behold the N78 comes up with v20.149 firmware after all. Something screwy obviously present there, but worth a good look over-the-air or via Nokia Software Update if you own an N78. Do a backup anyway, but in theory all your data and apps should be safe.