Historically, similar weapons have been used as early bombs in ancient times. Bombs made out of Greek Fire was used during the Medieval Ages by the Byzantine Empire.
The Winter War had Finnish soldiers use Molotovs to burn Soviet tanks. They were able to do this effectively by using skis to perform hit-and-run attacks in the mountainous and snowy climate of Finland. The Molotov was effective because Soviet tanks at that time were so crudely made that they had several gaps, which the flammable liquid could flow into.
WWII saw many uses of the Molotov Cocktail in all theaters. In the Battle of Stalingrad; Stalin ordered his army to maintain close distance to the enemy to prevent The Luftwaffe from bombing positions without causing friendly fire. Because of this urban combat; it was common for both sides to ambush enemy tanks with Molotovs.