I feel foolish having to ask this but then I should be used to that...
I have a KVM switch to share this old Acorn computer with a PC running XP. PS2 for the Acorn. On switching, the mouse sometimes goes apes**t on the PC - opening up all sorts of things.
What it has done is to make the toolbar double height and moved it to the top, rather than bottom. And I can't for the life of me find out how to move it back to the default size and position.