I use a 3Dconexxions Spacemouse, as well as a normal mouse. In Preferences/Move&View/OtherDevices the input device can be selected. It used to be remembered, so every time I started the viewer, I could use my Spacemouse.
The setting no longer sticks, so every time I start the viewer I have to go through the process of activating my Spacemouse again in Preferences.
This bug was introduced sometime recently-ish; I only noticed now because Firestorm's latest public release version now has the bug. So I guess the change was some time between Firestorm's previous public release, and this one. The issue never used to occur in either viewer before that; I have used a Spacemouse like this for many years.
This is something of a pain!