Lovely song - one of the translations has "mie" (in this context, sweetie) as Crumb, but it's (maybe also but I think instead) the word for the soft inside of the bread, in contrast to the crunchy outside. Pain de mie has no crunch to its outsides, but a good baguette would.

Mercerie is where you get cloth, like to make your own clothes, and needles and threads etc. Thimbles. Notions, I guess.

So a mercelot would be a traveling salesman of such notions, so yeah, haberdasher would fit.

Also I would translate the folding line as He folded her once, he folded her twice...