"upcoming account change" pop-up in Thunderbird

[Simes]

I am using Thunderbird 140.7.1esr (64bit) on Linux.
On starting Thunderbird, a pop-up box appears on the bottom left corner in red text saying
"upcoming account change"
with a button linking to more information.  Clicking on that button tried to take me to a mozilla web site which is giving an error:

Looks like there’s a problem with this site

https://support.mozilla.org/ sent back an error.

Error code: 406 Not Acceptable

• Check to make sure you’ve typed the web site address correctly.

It appears support.mozilla.org is not working, hence me posting here.

I think it may have been trying to link to: https://support.mozilla.org/kb/thunderbird-and-yahoo

Googling the error message gives one result and that is to a page on that web site too: https://support.mozilla.org/en-US/questions/1569758

Any idea what that pop-up was about and what is happening?  Is it something to do with Yahoo needing a new way of connecting?

[Simes]

(a)  The site  https://support.mozilla.org/  is still not responding.  Is it a fake site, nothing to do with Mozilla?

(b)  The pop-up has not returned - was it just some sort of phishing scam?

[Simes]

Is there anybody...

... out there?

I assume the message was a phishing scam and I'll forget about it.

As for  https://support.mozilla.org/  , according to the Wayback Machine, that hasn't worked since January.  Is Mozilla starting to fail?  Even trying to access it from the link on mozilla.org gives:

This page isn’t working

If the problem continues, contact the site owner.

HTTP ERROR 406

[Simes]

Even the Help Centre link from the Help Centre fails:

Looks like there’s a problem with this site

support.mozilla.org sent back an error.

Error code: 406 Not Acceptable

What can you do about it?

• Check to make sure you’ve typed the web site address correctly.
• The site could be temporarily unavailable or too busy. Try again in a few moments.