I am using librewolf, but I guess this extends to Firefox as well.
Is there a Settings page that acts sort of like the
Page Info > Permissions page. but instead of it only pertaining to a specific website, it acts as a preference setting for all websites like in
Settings > Privacy & Security > Permissions?
I went to a website that asked for HTML5 canvas image data and granted it for testing purposes, thinking I could remove it later in Settings. But I realized that the permission was not actually there, and I had to go back to the individual website and remove it.