Looks great! But as mentioned in another comment; where are my data stored?
Also, the free version seems pretty useless if there is no way for me to export my data and it only shows the three first lines of an annotation
Since you ask for feedback, here are some ideas:
* Group highlights from the same url
* Save all open tabs as a list
* Reader mode
* Archive the urls in my lists in some way; preferably as a single html file