FiraCode font does not display properly on VSCodium

Question

I am setting up VSCodium in my Manjaro KDE environment and I found out that my FiraCode font does not show properly in my integrated zsh terminal. This confuses me, because I thought that FiraCode has Powerline support. I also tried to use some other fonts instead from powerline-fonts, but those did not seem to load properly either.

This is what my integrated terminal looks like at the moment:

As you can see, a character fails to load on the left hand side. This is incorrect behavior as it does load correctly in my Konsole terminal.

This is what it should look like instead (picture is taken from my Konsole terminal):

My settings.json has the following contents:

{
    // zsh (with oh my zsh) as default
    "terminal.integrated.defaultProfile.linux": "zsh",
    "terminal.integrated.fontFamily": "Fira Code Retina",
    // Autosave
    "files.autoSave": "afterDelay",
    // FiraCode font
    "editor.fontFamily": "Fira Code Retina",
    "editor.fontLigatures": true
}

For now, I have no idea how to fix this issue nor what exactly causes it.