If you use uMatrix, you can easily block the localhost and local network "sniffing" with the following rule[0]:
  * 127       * block    ### block access to IPv4 localhost 127.x.x.x
  * localhost * block
  * [::1]     * block    ### block access to IPv6 localhost
  * 192.168   * block    ### block access to LAN 192.168.x.x
In principle, you can use this without any other blocking, i.e. with the rule:  * * * allow
and hence without disabling javascript on any sites.[0] https://github.com/ghacksuserjs/ghacks-user.js/wiki/4.2.3-uM...
Edit: as pointed out by DarkWiiPlayer below, if you want to be able to access the localhost websites from the same browser, you need:
  localhost localhost * allow
and similarly for the LAN. In full:  127       127       * allow
  localhost localhost * allow
  [::1]     [::1]     * allow
  192.168   192.168   * allow replies(7):