def fx_executable()

in conftest.py [0:0]


def fx_executable(request, sys_platform):
    """Get the Fx executable path based on platform and edition request."""
    version = request.config.getoption("--fx-channel")
    location = request.config.getoption("--fx-executable")
    if location:
        return location

    # Path to build location.  Use Custom by installing your incident build to the coinciding path.
    location = ""
    if sys_platform == "Windows":
        if version == "Firefox":
            location = "C:\\Program Files\\Mozilla Firefox\\firefox.exe"
        elif version == "Nightly":
            location = "C:\\Program Files\\Firefox Nightly\\firefox.exe"
        elif version == "Custom":
            location = "C:\\Program Files\\Custom Firefox\\firefox.exe"
    elif sys_platform == "Darwin":
        if version == "Firefox":
            location = "/Applications/Firefox.app/Contents/MacOS/firefox"
        elif version == "Nightly":
            location = "/Applications/Firefox Nightly.app/Contents/MacOS/firefox"
        elif version == "Custom":
            location = "/Applications/Custom Firefox.app/Contents/MacOS/firefox"
    elif sys_platform == "Linux":
        user = os.environ.get("USER")
        if version == "Firefox":
            location = f"/home/{user}/Desktop/Firefox/firefox"
        elif version == "Nightly":
            location = f"/home/{user}/Desktop/Firefox Nightly/firefox"
        elif version == "Custom":
            location = f"/home/{user}/Desktop/Custom Firefox/firefox"

    return location