You can fix THAT inventory problem by copying a specific file from the SL viewer into Firestorm. I have forgotten the name of the file but it is on the "lost inventory" page in the Firestorm wiki -- a ways down the list of things to try. It is a pretty easy fix. Had to do that for an alt maybe six months ago.
Inventory Issues
in Inventory
Posted
https://wiki.phoenixviewer.com/fs_missing_inventory#method_2_-_inventory_copy_from_sl_viewer