Useless!

The ribs and edges are thermal conductors that will completely cancel out any benefit of the foamed cores. If you're going to foam, foam the entire wall, or at least the rims and top four feet. And then you have to cover it an approved fire-rated material, such as 1/2" drywall.

Would I be better off putting up furring strips and foam board? If I do that would my stairs and drop ceiling need to be moved to insulate all of the wall?

You have to figure out the economics and convenience of materials and methods. Both are recommended by Building Science Corp.

The more of the wall you insulate, the better the results. The same considerations apply to the ceiling and stairs. Moving the stairs isn't usually practical. If the ceiling is the drop-in type, it's easy. If it's drywall and you have to cut out a two foot strip all around for access, it's an obviously much more expensive retrofit.

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To go back for a sec on the idea of filling the blocks with foam, even new blocks designed to be filled with foam only add R1 to the wall.

According to the US Department of Energy, Energy Efficiency and Renewable Energy, "Field studies and computer simulations have shown that core-filling of any type offers little fuel savings since the majority of heat is conducted through the solid parts of the walls such as block webs and mortar joints."

Here is a link that might be useful: Concrete Block Insulation

thanks for all the answers, and the link, The salesman, who has not come yet said foam filling the block will give the wall an r value of about ten or eleven, that means a hollow block wall already has a nine to ten r value?

Correction: only add R1 to the wall

That should read R1 to R2 per inch. But these are blocks that incorporate insulation in much more complex ways that simply filling the voids. Some blocks are manufactured with vermiculite in the voids. But the Department of Energy doesn't provide an R factor for these.
However, the Portland Cement Association says they are designed for Southern climates.

The R value of a concrete block wall is negligible--only R1.28 for a 12" block.