Drop it into your TiddlyWiki in another tab, at the green rectangle at the top that says “Drop here”.
That’s all! It will add itself to a “Plugins” category so you can easily remove it later. Edit the Plugins tiddler and remove “Contents” from it if you want to remove this category from the ToC (it will override the tiddler in the plugin and persist if you reinstall later).
This script will add a button on the libre.fm player that takes you to a download page for the current song. It also adds a box with a suggested name on the download page itself that you can copy and paste when saving instead of having to save the file as a bunch of confusing numbers (I couldn’t get the download attribute to work so you’re stuck with this instead :p; I will try to let you configure the format later with %a, %t, and that kind of thing if people need that), and adds default keyboard shortcuts for the play (s), pause (d), previous (a), and next (f) buttons via the HTML accessKey attribute (I’m probably going to add preferences later so you can change those without editing the script).
If you have a touch screen and it’s hard to hit the buttons you might also find this style useful: