Steps to reproduce:

In my Arch Linux installation, in order to support Colored Emojis in Applications like KDE Kate I have added Noto Color Emoji as the first font loaded by all Applications.

This is the configuration I have near the end of my ~/.config/fontconfig/fonts.conf file right before the <dir> block:

<match target="pattern">
<edit name="family" mode="prepend">
<string>Noto Color Emoji</string>
</edit>
</match>

This forces Noto Color Emojis to be the first font.

Actual results:

In Thunderbird 102 all my Numbers are Emojis: https://atvg.cc/s4RU5t and the Word-Spacing is huge: https://atvg.cc/sdjkH4dS.

This seems to occur because Thunderbird 102 does not fall back to another font for normal text.

After a bit more testing Firefox 102 also suffers from the same issue. I will only open this issue here because I first found it in Thunderbird.

Expected results:

Thunderbird 102 should use a fallback font for normal text like Thunderbird 91 and prior did it. Having Numbers: https://atvg.cc/scsaBdz and normal Word-Spacing: https://atvg.cc/syZqGZFm

I manually tested Firefox 102 down to the first version where it is not broken and found that this issue was introduced in Firefox 99.

So this is a Firefox issue?

Ha, yes perhaps. I hadn't read the comments
maybe something in https://mzl.la/3Av1M5i ?

(In reply to Alessandro Castellani [:aleca] from comment #2)

So this is a Firefox issue?

Both Firefox and Thunderbird are effected with this bug. I first found it in Thunderbird 102 and then later found that it also exists in Firefox 99 and up.

Would be a core issue yes.

The Noto Color Emoji font includes glyphs for the ASCII digit characters (and some punctuation), and for space, so if you force it to be prepended to all font family lists, that's what gets used. I'm not sure this can be considered a Firefox bug: it's doing exactly what was requested by the font configuration. (How is it supposed to know "Oh, I didn't really mean it for these characters, only for those ones...."?)

Well, I do not know how the application guesses what to do. But Thunderbird and Firefox (99 and later) have this issue. So something had changed between 98 and 99 to cause this. Every other application I have works without issue, including stock Thunderbird 91 and Firefox 98.

Sorry, there was a problem with the detection of inactive users. I'm reverting the change.

Here's reporter's screenshot 1

In Thunderbird 102 all my Numbers are Emojis: https://atvg.cc/s4RU5t

Here's reporter's screenshot 2

In Thunderbird 102 all my Numbers are Emojis... and the Word-Spacing is huge: https://atvg.cc/sdjkH4dS.

Reporter's screenshot 3: Same scenario in TB 91, numbers display normal

Thunderbird 102 should use a fallback font for normal text like Thunderbird 91 and prior did it. Having Numbers: https://atvg.cc/scsaBdz ...

Reporter's screenshot 4: TB 91, font spacing is normal (also note the icons in between)

Thunderbird 102 should use a fallback font for normal text like Thunderbird 91 and prior did it. Having [normal] numbers ... and normal Word-Spacing: https://atvg.cc/syZqGZFm

(In reply to Wayne Mery (:wsmwk) from comment #3)

maybe something in https://mzl.la/3Av1M5i ?

Yes...
Jonathan (:jfkthame) has already hinted in comment 6 that this is INVALID.
Jonathan's Bug 1759667 Comment 12 has the full explanation and history.
Which makes this bug 1777701 the 4th duplicate of Bug 1759667 (currently INVALID).

(In reply to Jonathan Kew [:jfkthame] from comment #6)

The Noto Color Emoji font includes glyphs for the ASCII digit characters (and some punctuation), and for space, so if you force it to be prepended to all font family lists, that's what gets used. I'm not sure this can be considered a Firefox bug: it's doing exactly what was requested by the font configuration. (How is it supposed to know "Oh, I didn't really mean it for these characters, only for those ones...."?)

AtjonTV (reporter), next time kindly attach your screenshots directly on the bug via Attach New File button above comment 0, for everyone's convenience :-)