If you read back through this thread you will find most of the answers for your questions , but to save you some time an ftf file is the whole(complete) firmware package for your phone as for the generic swiss label it only means that a. its generic and b. its from the swiss region of the globe i.e if your phone has been opened to work on any network then you can flash a generic firmware regardless of the area its for however if your phone is locked to a certain network then you must use the firmware that is for your phone ,for your country and for your network if it is not then you will softbrick your phone.
Firstly, thanks for the answer.
I have already installed Xperia M4 Aqua (E2303) 26.3.A.1.33 Switzerland Generic to my phone. It works.
To the thread starter, thanks for the firmwares.