It seems the portable launcher of that program can't fully handle the change of the drive letters. My profile was created when the USB drive letter was F and works perfectly with it:
(the tab size is the right since the TabMix Plus extension works)
(all the addons have their icons and their options menus are available)
When I put the drive on another computer and drive letter changes (to G for example), the picture changes as well:
(the tab size is longer, that means TabMix Plus doesn't work)
(some of the addons have no icons and their options menus are not available)
That happens with the last two major versions (55 and 56), not sure if it wasn't happening before, but it seems the portable Firefox is not as portable as it used to be anymore.
This is fixed in today's release. Some extension settings were moved to another file and that file needed to be portablized by our launcher.
Sometimes, the impossible can become possible, if you're awesome!