MSNBC Live

I don’t think you can get MSNBC live as a standalone app.  You can get MSNBC live if you subscribe to one of the cable replacement streaming services such as Sling TV or Hulu with Live TV.

There is a free NBC News app that contains some MSNBC content, but it's not live.  Peacock (not free) also has some MSNBC content.

While not the full MSNBC channel, your least expensive choice would be to subscribe to the Peacock streaming service for $5.99 per month.   You can watch Morning Joe live or recorded. Other MSNBC programming can be watched on a delayed basis.  News programs from NBC network are also available live or delayed.

You can download and install the Peacock App on your Firestick.