I don't know how many times already I've had to remove this, and now nothing seems to work anymore. Setting browser.newtabpage.activity-stream.newtabLayouts.variant-b to false should work, I guess, but it doesn't.
Edit: shishka_b0b has posted a solution (as for enlarging the quick link icons, I forgot the simplest solution - zooming in the page)
The CSS solution worked, thank you! And that guide was useful, now I'll have to toy with the CSS elsewhere too... :D
(The config you mention in the edit doesn't seem to work, however.)