Update: the extension is back on the web store for now, so you can install from the download page.
Once again Google have removed 23++ from the Chrome Web Store without offering any explanation.
To install the extension you’ll need to download and install it manually. To do this, follow the instructions in the post I made last time they did this but use this download link to get the latest version.
The current version of Chrome appears to have made this process even more difficult – if, when you do Save link As, Chrome tries to save the file as 23pp-2.1.4.bin, you’ll need to change the extension from .bin to .crx for the rest of the process to work.