Rated 4 out of 5 stars

Can you restore back the "hide thumbnails" button? Sometimes it's useful. If it'll be two buttons as in "Customize about:newtab" addon - it'll be better.

And I want an option to change filling mode of thumbnail as "fit to weight", "fit to height", "fill", etc.

Another request is option to set background image for the about:newtab.

And the bug. If it is a spacer (blank cell) between cells, then addon can't set the thumbnail for all cells after spacer.
Also here you can see the croped image in first thumbnail.

This review is for a previous version of the add-on (2.1.1-signed). 

I've fixed the last two, not sure about the best way to do the first two, but they are things I want to do.