BROWSER::
        Tells Newsboat what browser to use if there is no "browser" setting in
        the config file. If this variable doesn't exist, a default of lynx(1)
        will be used.

CURL_CA_BUNDLE::
        Tells Newsboat to use the specified certificate file to verify the peer.
        The file may contain multiple certificates. The certificate(s) must be
        in PEM format.
        +
        This option is useful if your libcurl is built without useful
        certificate information, and you can't rebuild the library yourself.

TMPDIR::
        Tells Newsboat to use the specified directory for storing temporary files.
        If this variable doesn't exist, a default of /tmp will be used.