I couldn't find any discussion on this specific subject and I'd like to list at least a hundred boxes on the marketplace. Magic box ain't required anymore and I'm on Firestorm viewer. How do I do? Thanks for your help.
All current viewers can use the Viewer Managed Marketplace.
Some third party viewers may not have the functionality if they haven't been updated since last summer.
I use Firestorm and they do have this capability. I've not had any issues doing this.
SL Viewer, Firestorm, and CoolVL definitely have VMM capability. Singularity is working on implementing it; I don't know if their test versions have it yet.
In SL Viewer and Firestorm you open a floater and work on your Marketplace inventory there. In CoolVL you drag and drop to the folder in your inventory and work on the items there.