Is Fiberboard sheathing under cedar siding ok with no vapor barrier

The moisture barrier would generally go between the furring strips and the concrete and would be attached to the wall simply by attaching the furring strips to the concrete. If you wanted to really seal the area you could run a bead of adhesive sealant between the moisture barrier and the wood.

6mil plastic is a "vapor" barrier, not a "moisture" barrier. The difference is that a moisture barrier allows air to permeate it but prevents liquid water from going through. A vapor barrier prevents water AND air being transmitted through it. Moisture barrier is used between porous materials like concrete and wood to allow the various materials to acclimate to changing temperature and humidity without exchanging liquid water (the concrete will absorb a lot of liquid water from the ground, and then pass it into the wood which is a sponge for water, which will cause the wood to rot). If vapor barrier is used, moisture will be trapped on either side of the barrier, which can cause puddles of condensation on the moister and/or warmer side of the barrier.

So, to answer your question, you should probably use a product like Tyvek or TyPar, or an older material like roofing felt, between the furring strips and the concrete. For an installation like this, you can just cut strips of the barrier to prevent direct contact between the materials, and then simply place them behind the furring strips as you attach the strips to the wall.

It depends on where you live and how you plan on attaching everything. For interior insulation you want the vapor barrier on the warm side so the colder regions would always do the interior facing and some warmer climates would do the exterior side of the insulation. The underlying rule of where would the moisture most likely be trapped still applies but it typically biased because of installation, how you plan on attaching everything. For interior walls, no vapor barrier is recommended if you use a full fill spray foam because it is a close cell foam (over 2lb density like most spray foam) and is meant to be a tight squeeze unlike most insulation and stops airflow instead of slowing it down. The same can be true for rigid foam especially for outside insulation. If you plan to use contact adhesive, liquid nails, etc glue to hold the rigid board to the house then you'll be essentially stopping all the air flow and that side would not be a candidate for a vapor barrier, additionally if you are gluing the siding on, the same rule would apply.

To sum up: If you are in a cold climate, even seasonally, it is a good idea to put a vapor barrier on the outside of the outdoor insulation as long as you are not gluing the next layer onto the insulation. This will help the trapped moisture wick out better.