This extension enabled me to get my big tiles back after the update to Firefox 60 botched them.
I like that I can just select to view 3 rows @ 4 columns.

After I replaced the tile previews with small jpg's I created from a screenshot the new tab page loads A LOT faster - it should not be necessary to do this yourself.

But after all that effort I wanted to backup my "new tab" configuration: unfortunately Firefox ALWAYS hangs.
After replacing the tile previews with jpg's it hangs with an incomplete zip of half the original size though.