The noun window shopping designates the activity of looking at goods displayed in shop windows, especially without intending to buy anything.

The earliest instance that I have found is from Our Philadelphia Letter, published in The Shenango Valley Argus (Greenville, Pennsylvania) of Saturday 6^th November 1875:

The tradesmen are brightening up the windows with holiday goods. The display is unusually attractive for this early in the season. A walk down Chestnut street is like a stroll through a museum of all sorts. To enjoy the feast fully, one must not be ashamed to do a little ‘window shopping,’ it need not matter if you run the risk of being looked upon as ‘from the country.’

The French equivalent of window shopping is the masculine noun lèche-vitrine(s), from the verb lécher, meaning to lick, and the noun vitrine, meaning shop window.

The earliest instance that I have found is used in the sense of window shopper; it is from Mon Pays sera le plus grand (My Country will be the greatest), a novel by the otherwise unknown Louis Dumas, published in the Mercure de France (Paris) of Monday 15^th August 1932:

Mme Lionel et sa fille Marie, s’étant arrêtées à la devanture d’un magasin, entendirent chuchoter derrière elles : « Voyez donc les lèche-vitrines ! Elles ne peuvent rien acheter et elles se contentent de coller leur nez sur les verres. »
     translation:
Mrs Lionel and her daughter Marie, having stopped at the window of a shop, heard whispered behind them: “Look at the window shoppers! They cannot buy anything and they content themselves with pressing their noses to the windows.”

The verb crébillonner, or crébilloner, meaning to window-shop, is peculiar to Nantes, a city in western France, on the River Loire; it is from rue Crébillon, the most exclusive shopping street in Nantes, named after the French playwright Prosper Jolyot de Crébillon (1674-1762). Paul Eudel (1837-1911) defined this verb as follows in Les Locutions nantaises (A. Morel publisher, 20 rue Crébillon, Nantes – 1884):

Crébillonner. Faire le beau dans la rue Crébillon.
     translation:
Crébillonner. To strut about on Crébillon street.