My guess is that Apple, as usual, doesn't grant thirdy part developers access to some parts of their software so is harder to develop extensions and some tipe o

My guess is that Apple, as usual, doesn't grant thirdy part developers access to some parts of their software so is harder to develop extensions and some tipe of features are even impossible to be implemented. Instead Firefox is open source and Chrome is partially open through the Cromium project (I think that most of the soure code is open but I don't know exactly how much so I could be wrong) so for these browsers is easier to develop useful extensions.