I also heard about using Molotov cocktails in 1939 btw. they were invented during Spanish civil war.
according to this discussion
http://www.historycy.org/index.php?showtopic=34280 unfortunately in polish only but I try wrote summary here they were use rather in second part of September campaign when situation start to be more desperate. They were use against soviet and German tank especially in town fighting examples Grodno, Wilno, Białystok, Pińsk, Kowel. Is know story about 2psk (Wołyńska BK)[cavalry brigade] in 3/4 of September during fight near Kamieńsk use this bootless. They destroy 30 tanks and 16 cars from 1DPanc. gen. Hans Schmidt. 49 Huculski (Mountain infantry) destroy many vehicles from SS "Germania" with use of Molotov in last days of September. In book about Army "Prusy" on page 123 there is info about infantry company equipped with Molotov against tanks. In 9th of September Polish high command release instruction for fighting with tanks. There are mentioned IED build from mines and bootless with fuel. In book "Wojna Polsko-Sowiecka 1939", s. 89 was mentioned that in 11th before soviets starts war companies on eastern border in that area has a training in use of Molotov against tanks based on experience from first days of war. There is also story from Army "Pomorze" that they use such Bootle's when they spend all grenades they were use in defence of Koronowo near Bydgoszcz in 2th of September. I can said that Molotov wasn't standard equipment of polish pre-war units but they start to be used more intensive during September as campaign progress. I also herd that soviets tanks in 17th because they progress so fast often they attacking without infantry in narrow streets of towns in eastern Poland often were welcomed with Molotov's falling from windows on their engines.