Dear Hiroki, I think its the best add-on in its category.
1. Notes are really stuck / related to tabs-pages.
2. Very convinient access to and management of all notes from the side bar.

Request to the developer:
1) allow for changing default notes' color. Now I can only set a color for each note individually.
2) allow for change default font size
3) allow to make note stay on screen while scrolling the page