It works fairly well as a basic epub reader. I wish this has more setting options. Thanks.

Really like this one. EPUB Reader, my old favoriate, had trouble with some epubs as it would cut off the last 4-5 lines of each chapter. This reader seems to work fine. Automatically goes to 2 columns if the window is wide enough, or you can force it to show one or two pages. Has book marks, adjust font size. The only color changes you have are 3 premade schemes: light mode, dark mode, sepia mode. No web mode (where you scroll vertically through a whole chapter), it has page mode only.

It's just basic add-on, that can be developed, anyway it looks better now, than many other ones.

I hope there will be possibility to open books online without of downloading (like pdf ones).