Found in

• Nightly 106.0a1

Affected versions

• Nightly 106.0a1
• Firefox 105.0b9
• Firefox 104.0.2
• Firefox 102.3.0esr
• Firefox 91.13.0esr

Tested platforms

• Affected platforms: macOS 11.6, Windows 7

Steps to reproduce

1. Log into your Outlook account.
2. Attach a PDF file to a new email.
3. Click on the pdf file for Preview.
4. Click on the "Open in new window" option on the preview window (located in the upper right corner).

Expected result

• The pdf file should be rendered correctly in the new window.

Actual result

• The characters of the pdf file are broken. Please see the screen recording for more details.

Regression range
Not a recent regression, I'll look more into it as soon as possible.

This is an old regression, the characters were properly shown on Firefox 63.0a1 - Build ID: 20180904100126.
Narrowed regression window to:

• last good: 7d542c1d11cd71d29efae6743780254d1db7c203
• first bad: bade35bc346f3bc1f5e8b59d3d49c7a1ba28166c

Pushlog Url: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=7d542c1d11cd71d29efae6743780254d1db7c203&tochange=bade35bc346f3bc1f5e8b59d3d49c7a1ba28166c