Sorry, I just watched the video. I think I might be doing too much guessing here (like that ever stopped me), but Nokia's probably using the gecko engine system wide. There might be some of what I mentioned above going on, but that video suggests that the gecko engine needs some fine tuning. Mozilla does great work, but I'm not sure they have the right speed formula yet for these devices.

And what about Harmattan? I can't see a gecko-based flagship browser surviving when QtWebkit is a core library. This must have been Nokia's plan all along with the engine abstraction layer. Obviously a great move, and maybe this should be a high priority for the community. Time to resurrect that stuff.