The secret of Greek fire was lost - how is debated.

Some say it was lost during the sack of 1204, others that it had already been lost as the natural occuring surface oil wells along the Georgian Black Sea coast dried up - the petroleum from Georgia, according to these theories, were a vital part of Greek fire and without it, it could not be manufactured.

Yet others sources speculate that while Greek fire was not produce, the Byzantines still knew how to make it up to the fall of Constantinople 1453.

Naphta, that was used around the Mediterranean was not Greek fire, even if it shared some of its properties.

Regardless how the secret was lost, Greek fire was no longer possible to produce when the western powers started to build large artillery ships in the 17th century and onwards.

As for using naphta loaded hollow balls, it could have been possible, but not for cannons. While mortars could fire hollow balls (most often filled with gunpowder and shrapnel as explosive shells) that could have been loaded with naphta, cannons most often could not - they relied on a high muzzle velocity and thus powerful charges that very well could destroy a hollow ball before it had left the muzzle of the cannon, causing severe damage to the gun, the crew and their ship. It took until the 1830s until metallurgy had reached a point at which cannons could fire explosive (ie hollow) shells.

So, to summarize. Greek fire had been lost. Naphta was not as effective, and when European militaries used hollow shells, it was from mortars, which fired indirectly and was too inaccurate against moving targets at sea.