repair text encoding - enabled always by setting

[FF_LongTimeUser]

I have emails arriving from my home automation, where I want the degree symbol (°) (Alt-248 on numpad) to appear. However they get garbled by some mismatch in the encoding that I cannot correct. It looks like this:

°C

If I manually select View -> Repair Text Encoding, it looks as it should again.
I'd like to have the Repair Text Encoding feature "Always enabled", so it looks as it should immediately.

Thanks!


Parts of the source (removed antispam headers and a lot more):

Delivered-To: bla-bla@gmail.com
Received: by 2002:a17:907:11c6:0:0:0:0 with SMTP id va6csp278245ejb;
Thu, 29 Jun 2023 23:00:28 -0700 (PDT)
<bla bla>
Received: from mail-wm1-x336.google.com (mail-wm1-x336.google.com [IPv6:2a00:1450:4864:20::336])
by blabla (Postfix) with ESMTPS id 4ffff
for <a@b----.c...>; Fri, 30 Jun 2023 08:00:02 +0200 (CEST)
X-Received: by 2002:a1c:7415:0:b0:3fb:416d:7324 with SMTP id p21-fb416d7324mr1718678wmc.6.16885;
Thu, 29 Jun 2023 23:00:01 -0700 (PDT)

mime-version: 1.0
subject: Update
date: Fri, 30 Jun 2023 06:00:00 -0000
from: "house"
to: "Bla bla " <email>
content-type: text/plain; charset="iso-8859-1"
x-mailer: Socket 2.0.2

House Update
=============================
2023-06-30 08:00:00

Inside
Current Temperature: 21.68°C (diff 1250 s)
Dew Point Fast: 12.6°C

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[E-Rik]

I REALLY like the Repair Text Encoding feature/option; just found it and it sure saves me trouble on some old web pages: no more trial and error with the various encodings. Much appreciated! May God bless the work you all are doing there. ~ esn