`-->` in "Page not found" page is displayed badly on Firefox

[jasonren0403]

Summary

In "Page not found" page, --> string in article header is displayed weirdly in Firefox 138.0.4(maybe ligature problem), Edge 136.0.3240.76 was displaying properly

URL

https://developer.mozilla.org/zh-CN/docs/Web/HTML/Guides/Comments
https://developer.mozilla.org/ko/docs/Web/HTML/Guides/Comments

Reproduction steps

1. Open any url with fallback link point to HTML guide comments page(instead zh-CN you can use any other language which don't get the translation already)
2. Observe the article header "Using HTML comments"

Expected behavior

--> string displayed properly in Firefox

Actual behavior

--> affected by ligature

Device

Desktop

Browser

Firefox

Browser version

Stable

Operating system

Windows

Screenshot

• currently it's displaying well in Edge
  

• and displaying badly in Firefox
  

Anything else?

No response

Validations

• I have read the Community Participation Guidelines.
• I have verified that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• I have checked that this is a concrete bug. For Q&A open a GitHub Discussion.

[caugner]

For the headings, we fixed this in #12134.

I will include this for consideration in our new front-end.