When reading about an artist, you can select a song or album, right-click it and perform a search in the Spotify application (http://www.spotify.com).
You can search by artist, album or song. Select any text, search and the result will be displayed in Spotify.
To be able to use this addon, you must make sure your browser can handle Spotify-URI:s (spotify://).
If you are using Linux, you must follow this guide (http://www.spotify.com/en/help/faq/wine/#Opening_spotify_URIs_from_browsers)
Using bookmarklets you can get a similar functionality without installing this add-on. To try this, create a bookmark in your "Bookmarks Toolbar" and name it e.g. "Artist search" and in the "Location"-field paste something like this:
Now you should be able to perform a Spotify search by highlighting an artist name and clicking on this bookmark.