iPhone browser settings

Depends upon what other 17+ apps you are referring to. In just selecting Firefox as the default browser in Settings>Firefox>Default Browser App most everything will open in Firefox. There may be a few Apple apps that will still open in Safari, those will be few, and will have to do mostly with settings. You can always offload Safari to stop that (Settings>General>iPhone Storage> than scroll and select the app you wish to offload> than select offload [or delete] app, then repeat for each app)(offloading will disable the app, but leave a small amount of it’s data behind for quick reactivation whereas deleting will do just that and it would need to be re-download if needed). But keep in mind that you will no longer be able to access the feature(s) in those apps that relied upon Safari to work. And dependent upon which particular other apps you are referring to, most of those may also be safely offloaded as well, but again, some may affect other features of the phone. Although any offloaded or deleted app may be fairly quickly, temporarily, re-loaded in order to access whatever features they have disabled in order to re-enable that feature.

Hope that helps. In order to be anymore specific than that, would need to know exactly what apps the “17+ apps” are, and possibly, your reason for “blocking” (or disabling) each one would be.