To disable the Firefox DNS cache, go to about:config in the address bar.
– Right click to select “New†-> “Integerâ€, enter “network.dnsCacheExpiration†as the preference name and “0″ as the integer value.
– Create another new integer called “network.dnsCacheEntries†as preference name and again enter “0″ as integer value
There is no facility to clear it, but possibly doing the above, then removing it again, could clear the cache.. Didn’t try it – just disabled it. My resolvers are on the local network so they can cache it for me – this way they ‘ll actually have something to do 😉