Bug 2021366

Created attachment 1840789 [details]
look at "affiliation"

Description of problem:
I visited https://schema.org/Person in Firefox in Fedora 35 KDE spin and noticed the monospace text "affiliation" was not monospaced; the letters "ffi" were on top of each other as if replaced by the ligature ffi.

The page CSS is styling the <code> tag "font-family: Courier, monospace;", and in Fedora 35 KDE Spin `fc-match Courier` returns
   NimbusMonoPS-Regular.otf: "Nimbus Mono PS" "Regular"
indeed, if I set font-family to "Nimbus Mono PS" in some simple HTML https://www.skierpage.com/bugs/nimbusmono_not_monospaced.html , other ff combinations are also "ligature-ized".

I tried these two URLs in the chromium-browser package and in the Epiphany and Konqueror browser flatpaks. These did not use "Nimbus Mono PS" as the fallback font for font-family "Courier" so did not display "affiliation" badly on the Person web page, but if you specify font-family "Nimbus Mono PS", you get the ligature.

Version-Release number of selected component (if applicable):
Mozilla Firefox 94.0
urw-base35-fonts-20200910-9.fc35.src.rpm

How reproducible:
Always. 

Steps to Reproduce:
1. Visit https://schema.org/Person and https://www.skierpage.com/bugs/nimbusmono_not_monospaced.html in Firefox and other browsers.
2. Note how "ffi" appears.

Actual results:
Firefox uses "Nimbus Mono PS" as the fallback for font-family Courier; all these browsers replace "ffi" and such with the ligature character in "Nimbus Mono PS", destroying the desired monospace effect.


Expected results:
Monospaced fonts should appear... monospaced, so every character should occupy the same amount of horizontal space. However, if a font provides ligature glyphs for "ffi" and such, then it's unclear if it's wrong for the browser to use them; (l33t developers now explicitly use monospaced coding fonts that do wacky substitutions.)

So the fix could be for Firefox and/or fc-match to _not_ use Nimbus Mono PS when  text handling requests Courier. The other browsers on my system don't, I'm not sure why. Another could be to remove the ligatures from Nimbus Mono PS.

Additional info:

The rendering of code on that page (see attachment) is pretty terrible, note the oversized 'd's in "address". Another reason to have Courier match some other monospaced font than Nimbus Mono PS.

You can use the Fontmatrix program to enable OpenType features; checking latn > dflt > liga changes the display of "ff" combinations.

Firefox using ligatures in monospaced fonts is https://bugzilla.mozilla.org/show_bug.cgi?id=384395 , was closed WONTFIX "We can't really do anything about it -- the underlying text system is doing the ligaturization, not us".

ArchLinux users discussed the problem in https://bbs.archlinux.org/viewtopic.php?id=238832