Is a boycott an effective mean of protest?

Effective depends on how many people join in. Let's say you, just you would decide to boycott McDonalds, Adidas, Levi's, Coca-Cola or something like that - well, they'd never notice. But let's say you managed to convince a whole suburb to boycott McDonalds, then at least the local restaurants would notice it.

And fair or not is difficult to say. If you're boycotting a chain because of something that happened at one of the outlets, then it isn't particularly fair because you're "punishing" a business that didn't have anything to do with the original event.

But at least it's legal. Taking your business elsewhere isn't a crime.