The command { thunderbird 'news:news.answers'; }

I have no idea what you're talking about.

You'll need to create a news account for the news server of your choice. Then subscribe to the group(s) you're interested in.

I am talking about launching Thunderbird from the command line.

thunderbird -news news://server/group

see https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options

That URL is wrong, news URL do not have the authority part. The semantic of this URL is to open the group in the default Usenet server. The command { thunderbird -news 'news:news.answers'; } opens Thunderbird but does not show the group.

The command line is handled the code in nsMailNewsCommandHandler.js; the expression (neckoURL.messageHeader) causes an invalid value exception, probably because it expects a message reference, not a group reference (represented by msgKey == -1 in nsMsgDatabase::GetMsgHdrForKey). It looks unimplemented.

Reported as bug 1096355

According to the examples in the applicable standards document RFC 3986 Section 1.1.2, "news:comp.infosystems.www.servers.unix" is a valid URL. Thus,

• thunderbird news:comp.infosystems.www.servers.unix

should work similar to

• thunderbird mailto:John.Doe@example.com

The command-line syntax is the internal syntax, but without the "-news" switch, you'd expect the URL passed as argument to be parsed.