azure serial console display garbled when accessing through firefox

Hi,

Using firefox (latest) on either freebsd-stable/13 or on linux mint, when 
accessing the virtual console on azure, rather than displaying readable 
letters and numbers as is usual, the display just shows multi-coloured icons 
where each character should be.

Turning off hardware accelleration doesn't fix the problem. I've also tried
"firefox --safe-mode --no-remote" but the problem remains.

The console works fine using www/dooble (dooble-2022.02.15)

Is this a known issue? I'm asking here rather than at firefox because, 
as I understand it, firefox under linux and firefox under freebsd are very similar.
Do I need to raise the issue directly with mozilla?

The version of firefox under freebsd is firefox-98.0.2,2 and under linux mint it's 
"Mozilla Firefox 98.0.2"

thanks,
-- 
J.