The SMG v2.17 release is bigger than our usual releases as it makes it a lot easier to work with browser-based music players like SoundCloud and YouTube. To make these changes possible, we have to remove the Groovemarklet and update the SMG-web plugin; we made a change to how the SMG appliation communicates with the browser, and this means that from version 2.17 onward, the Groovemarklet won't work anymore.
On this page, you can find how to update your SMG installation.
Note that the web extension is only available on Google Chrome. We intend to support Firefox in the long term, which is why we're not removing the Groovemarklet right now, but Firefox is not supported during the writing of this page. If you need to use Firefox, please stick with the Groovemarklet for now. We will delete the Groovemarklet once we support Firefox, our aim is to make this happen before the 1st of October.
To update, all you have to do is update your SMG installation.
The plugins are only necessary when you want to read music from browser-based music players, like YouTube, SoundCloud, di.fm and others. If you don't use any of these, it's not necessary to update right now. It is recommended to update regardless.