odd issue affecting firefox (any version) on freebsd (any version)

[tech-lists]

Hi,

This is a really odd problem which I haven't a clue how to debug.

I use fastmail.com for my email. Sometimes, I'll want to use a web browser
(firefox in this instance) to look at mail via their webmail. I have, amongst
other machines, my main desktop machine running 12-stable/kf5/plasma.

If I use firefox at the site to compose email, I can compose it but when I try
to send it I get "sending failed" and this is real, the mail is not sent. If I
run firefox (same version) from an ubuntu machine, I *can* send mail.

If I run iridium on the desktop machine and do the same thing, I *can* send
email.

I have tried this from a pristine freebsd-current vm as well. I get the same
result as I do from my freebsd-desktop. That machine, as it's a vm, does not
run a DE.

fastmail support haven't a clue about this issue, not that I'd expect them to
in this instance as it's far outside of their support remit.

So why can I not use *specifically freebsd firefox* to send email from
fastmail.com's webmail? How can I debug this? Is it a headers thing?

thanks,
-- 
J.
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