Last.fm recently updated (more like downdated) their UI. Now, to be able to view and write comments, you have to refer to a separate URI. This Tampermonkey script brings back the old feel of the shoutbox.
Using this script, it is possible to comment, like, and view comment sections without leaving the artist's page. Replying to comments will take you to the shoutbox location.
Create a new Tampermonkey script and paste the entirety of this JavaScript code into the Tampermonkey code box. Make sure the script is active when visiting last.fm as indicated by a red dot in the Tampermonkey extension icon.