It sounds more like a SourceForge issue than FileZilla. SourceForge used to provide clean binaries, but I guess they changed that process in the past year or two to bundle apps in the installer wrapper. You need to be extremely careful during the installation process to make sure that you do not accidentally install some extra software. The same happen to uTorrent - they also added tricky question during the install process to include advertisement, change default browser and such. That's a sad way to earn money - the end-users will definitely move on because of that.