I think in for the majority of the 18th century it was just a name distinction.
Oh, and they often wore different uniforms.
If you're reading about Frederick, you might find fusiliers wore different headgear from other line infantry.
Also, I think their minimum height was lower.

There could be a prestige issue as well, but that's more likely to do with the length of a regiment's establishment, rather than its classification as fusilier or musketeer.

I think originally Fusiliers would have had higher prestige, as the flintlock was better than the matchlock.