Rated 5 out of 5 stars

Just great! The thing, I've looked for! Thanks.

Paradiso: use url "chrome://qfnotes/content/editor.xul" to make a bookmark, which will open editor in tab.
Urbane.Tiger: Same trick actually gives an opportunity to open it in a side bar... I'm not using it, though...

The only complain is that this yellow icon is somehow annoying.. too bright or something... I had to tweak it, and now it's just perfect :)

This review is for a previous version of the add-on (0.4B).