Thanks for the careful feedback. In the current version, "right" and "left" still mean tabs/groups strictly to the right or left of the clicked item, but there are separate menu items for "clicked tab/group and tabs/groups to the right" and "clicked tab/group and tabs/groups to the left".

The selection-related defaults have also been improved: "Choose tabs/groups" is enabled by default for new installs, and the latest version adds a separate "Selected Tabs" item for tabs selected directly in Firefox's tab bar. Existing custom settings are preserved, so users with customized move targets may need to enable new items manually.