Why does the browser use Courier instead of Consolas for "font-family: Consolas, Courier", although Consolas is available through fonts-conf replacement?

Question

Why does the browser use Courier instead of Consolas for "font-family: Consolas, Courier", although Consolas is available through fonts-conf replacement?

I am using Iceweasel (rebranded Firefox) browser on Debian with XFCE4.

I defined the alias rule in my ~ / .config / fontconfig / fonts.conf file.

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <alias>
        <family>Consolas</family>
        <prefer><family>DejaVu Sans Mono</family></prefer>
    </alias>
</fontconfig>

The conclusion fc-matchconfirms that Consolasit will now be replaced as DejaVu Sans Mono.

lone@debian:~$ fc-match Consolas
DejaVuSansMono.ttf: "DejaVu Sans Mono" "Book"
lone@debian:~$ fc-match Courier
n022003l.pfb: "Nimbus Mono L" "Regular"

Now see the following browser output for JSFiddle: http://jsfiddle.net/yyvgcw02/ .

enter image description here

The above screenshot shows that the browser used correctly DejaVu Sans Monofor Consolasand Nimbus Mono Lfor Courier.

However, I expected it to use DejaVu Sans Monofor Consolas, Courier, but the above output shows what it used Nimbus Mono Lfor again Consolas, Courier?

DejaVu Sans Mono Consolas, Courier, Consolas , , .. DejaVu Sans Mono, ?

~/.config/fontconfig/fonts.conf . fc-match .

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <match>
        <test name="family"><string>Consolas</string></test>
        <edit name="family"><string>DejaVu Sans Mono</string></edit>
    </match>
</fontconfig>

, . binding="strong" edit, , ~/.config/fontconfig/fonts.conf, DejaVu Sans Mono font-family: Consolas, Courier, .

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <match>
        <test name="family"><string>Consolas</string></test>
        <edit name="family" binding="strong"><string>DejaVu Sans Mono</string></edit>
    </match>
</fontconfig>