Johnson had been responding to comments that Hollande would not be prepared to give the UK a better deal outside the single market than it had in it.
Hollande's message was repeated by Maltese Prime Minister Joseph Muscat who, in a speech to the European Parliament on Wednesday, said any post Brexit deal had to be "less desirable" than EU membership.
Downing Street defended the foreign secretary, insisting he wasn't comparing the French President to a Nazi.
But, in a tweet, ALDE group leader Guy Verhofstadt criticised Johnson, saying, "Yet more abhorrent and deeply unhelpful comments from Johnson which Prime Minister May should condemn."
Further scathing condemnation came from the former UK Europe minister and Labour MP, Denis MacShane, who told this website, "In the world of politics, words mean something. In the world of Boris, words mean nothing."
He added, "He sees himself as a Harry Houdini of his own mouth and pen ever able to escape responsibility for his weather vane political utterances.
"It scarcely matters save that Johnson is Her Majesty's principal secretary of state for foreign affairs and that used to be a job in which words were weighed carefully, as an utterance by the British foreign secretary once mattered in the world.
"Now everyone knows that Boris has his fingers crossed behind his back whenever he speaks or writes and that was he says today will be inoperative tomorrow.
"It may amuse some but the end result is that the most cynical of all the hardline Brexiters is doing serious damage to his country as overtime Boris open his mouth someone somewhere sells sterling or decides that Britain does not have a serious government whose word can be trusted.
A senior Labour spokesperson said, "We are all aware that the Foreign Secretary has a habit of making wild and inappropriate comments.
"Talking about World War Two in that context is another one of those and that is not going to be something that is going to improve the climate for this negotiation."