I think we are thinking along the wrong lines, and the evidence we need is really in front of us...
We know molotov cocktails work, we've all seen grainy news footage of French students in the late 60's, and N Ireland in the 80's. A Molotov cocktail "works" because it transports a combustible substance or liquid, is sufficient volumes, to the destination, as well the ignition method. There would seem to be little point in dousing a tennis ball in petrol, and sending it off to the target, because it carries only a small amount of fuel.
What we need is a volume of fuel in a sufficient quatity that it will ignite the target, and not be used up on the way there, hence the idea about small, stubby French type beer bottles.
Another way, from high school days, is to take an empty co2 cartridge, drill a .22 hole in the round end, plug the base with a dob of solder, then fill with black powder, shot gun cartridge cordite etc, and then press a rim fire .22 blank into the .22 hole. It WILL land bulbous end down, ignite the blank, and the charge inside. Watch for shrapnel.
Bonus for slingers, they are small and aerodynamic. This information is for reading entertainment only.