Thanks -- I didn't realize that reordering tabs had been fixed. It only works on the active tab[1] and I guess I've only ever tried moving inactive tabs before. It's not perfect, but so far seems better than in Edge (which allows reordering of inactive tabs but is often rather janky) and Chrome (which has no ability to scroll the tab bar, so tabs quickly get uselessly tiny).

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1362065#c57