It literally isn't. Literally, "on" doesn't translate to "en", as it literally means "in". Literally, the "masse" in French here doesn't refer to literal "mass" as in a quantity of literal matter to be literally measured, but literally an uncountable concept like a literal crowd, for example.

So, which mass are you quitting on?

And in any case, to be literally correct the expression taken from another literal language should be literally italicized.