I accidentally allowed YouTube to access the data on a canvas. How do I disable a website from access a canvas?
By default, Tor Browser forgets about permissions when you close it. You can easily check it by revisiting Youtube (and see if it asks for permission again).
permissions.memory_only preference is set to false (default is true), Tor Browser stores permissions in a file named
permissions.sqlite in the profile directory.
If you have this file and it's modified recently, you can use a program like sqlitestudio to selectively remove existing permissions.
If you want to remove all existing permissions, removing
permissions.sqlite file should also do.