# set as ~/.config/fontconfig/fonts.conf
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <match target="pattern">
        <test name="family" compare="eq">
            <string>Fira Code</string>
        </test>
        <test name="prgname" compare="contains">
            <string>gnome-terminal</string><!-- replace with program name -->
        </test>
        <edit name="fontfeatures" mode="assign_replace">
            <string>calt off</string>
        </edit>
    </match>
</fontconfig>

# Other one
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
  <match>
    <test name="prgname" compare="contains">
      <string>gnome-terminal</string>
    </test>
    <edit name="fontfeatures" mode="append">
      <string>calt off</string>
      <string>clig off</string>
      <string>dlig off</string>
      <string>liga off</string>
    </edit>
  </match>
</fontconfig>