We usually fallback to treating /path as /path/ if the first one fails to return any content.
However, one case where we don’t do this is when /path looks like the path to download a file. waterfox-G3.1.1 looks like a path to download a file and that’s why you see the difference between waterfox-G3.1.1 and waterforx-G3.1.1/.
Adding a rewrite rule for this path should ensure both /path and /path/ have the same behaviour.