Here's his piece from yesterday's New York Times.
Theoretically, the efficiency and outcomes of a carbon tax and a cap & trade system should be the same. Practically, the tax requires us to "get the price right" while the trade system requires us to "get the quantity right".
Friedman seems to be arguing for the tax on the grounds of political acceptance, which is usually the opposite of what we hear. One of the main arguments against a carbon tax is that it contains the word "tax", which will immediately turn people off. Considering the recent debacles in the financial world, the black box mystery of cap & trade might indeed be more of a turn off.
He also argues for having the discussion of carbon policy be framed in terms of national security rather than in terms of climate change. I agree with this, though I'd add saving money at the household level to that thought. Those that don't believe that humans are affecting the climate aren't going to change their minds very easily, so telling them that the tax will help a problem that they don't believe exists is a waste of time. If however, you can argue that the same actions will make us better off as a nation for other reasons and save them money, then you're more likely to get buy-in.
Friedman handles the macro concerns nicely. For the micro, driving a fuel efficient vehicle, re-using plastics, composting veggie waste in your garden, eating less meat and using less water will save you lots of money. No one can argue against that, no matter what they believe about climate change.