Re: re. " ... the dumb pipes they really are ..."
Save us from manufacturer and operator app stores.
What will happen with Firefox OS and Ubuntu is what has happened to Android. The operators and manufacturers, in the mistaken belief that we actually give a pair of dingos' kidneys about their brands, will install an app store on their devices and everyone will just use the official Firefox/Ubuntu app store instead as it is cheaper to buy things from, better designed and/or they have more apps on it.
Some of the dumber manufacturers and operators will see that no-one is using their app store and decide that the solution to that problem is to make their app store the only app store on the device, and will therefore only sell to less technically-savvy customers who probably won't buy any apps anyway.
I used to think that eventually the operators and manufacturers would have to give up and focus on their core strengths of making decent hardware / providing a reliable dumb data pipe, but it seems that they're going to keep going round in circles with this "we want to own the platform" rubbish for the foreseeable future.