I found some quick and easy way (two settings to add in
about:config) on how to disable DNS caching in Firefox:
network.dnsCacheExpiration (integer) = 0 network.dnsCacheEntries (integer) = 0
If you have tons of Firefox windows with even more tons of tabs open like me and being in the need to tweak host’s IP address while a site is moving, this prevents you from re-starting the Fox. The setting is working immediately.