firefox runs for one user, not another

[steve%prd.co.uk@localhost (Steve Blinkhorn)]

I have an irritasting problem with firefox 120.0.1.  It runs fine when
I'm logged in as myself, but fails to start up when I use any other
login account.  The specific need is to run wearing my accounting hat
in software that periodically needs to re-authorise with tax
authorities.  Thjis has worked in the past, but probably with an
earlier version of firefox - the need only comes around every couple of
years.

At startup I get the NetBSDF workaround message, then:

ATTENTION: default value of option mesa_glthread overridden by environment.

thene either  "channel error" or "console error ({}), usually but not
always after the first glimmerings of an X window that looks as if its
going to be a browser window, that then goes away.

Is there some sort of setup I should be doing?

-- 
Steve Blinkhorn <steve%prd.co.uk@localhost>