Disable GetAddons pane on about:addons
We don't know which extensions Mozilla is showing to users and we are generally of the opinion that Tor Browser should not used with additional extensions. We can make it harder for users to shoot themselves in the foot by just hiding the GetAddons pane with extensions.getAddons.showPane set to false.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information