Plugin for Firefox, and Chrome - load in debugging mode.
Shows details of last hand, on right-hand side of screen.
Tested in 4p & 3p, firefox & chrome
Unzip into a dedicated folder on your local machine.
In Firefox: paste this into your address bar: about:debugging#/runtime/this-firefox, and Load Temporary Add-on. Find the manifest.json file in the dedicated folder.
In Chrome: go to chrome://extensions/ . Switch Developer mode on (top-right corner). Then "Load unpacked". Then find the dedicated folder where you unzipped the github zip file
Then in a new window, load https://tenhou.net/3 or https://tenhou.net/4
The scoring pane works on game logs as well as live games. Stepping through the results in a game log is the easiest way to test this extension. Go to the start of the second hand, or later, and then go back one turn - that takes you to the end of the last hand.