If you updated from 2.3.17 or 2.3.19 (an alias for 2.3.17 in AMO), please see the 2.3.18 release notes as there are many changes.
Notable changes since v2.3.21:
- fix import (broken in 2.3.21)
- UserCSS config dialog: show
(i)icon with a tooltip for@varwith a line break in its label like "Text for label \n text for tooltip"
Full Changelog: v2.3.21...v2.3.22
P.S. AMO review is very slow, v2.3.21 is still pending...