Thanks for the comment, this add-on exists only since yesterday night! For now it is very sketchy, also due to some limitations of the young Web Extensions API (e.g., it is impossible for now to have a "Load file" window appearing when clicking an item in the small pop-up menu)...

The first features I want to add are mainly related to the possibility of loading back saved tabs (both by pasting a list of URLs and by loading a text file). The other ideas you listed seem indeed interesting and I will consider them when I get some time to invest in developing new features!