I've been poking around for alternatives to SuperStart that work with Firefox 57, and chose this one because it seemed like the best match.

... That said, while I was aware grouping wasn't a feature, I didn't think simply rearranging sites would mean wiping them all out and re-adding them sequentially in the order I want them in.

While using it, it blipped out of existence, so I'm writing a bug report about that now.