Firefox updated to FF 57 and I really don't like the first version so I went back to FF 56 and clicked "check for uploads but allow you choose to install them". Next time I closed/opened Firefox it loaded 57 without so much as note.

So, how I prevent this happening again? Having to reload the earlier version isn't particularly big thing, but if I have to do it every time I close FF it gets old and fast. If it comes to that, what I should do in about:config to change things?