Disabling the DNS cache of Mozilla Firefox
The Firefox web browser contains its own DNS cache independent of your operating system. For most users, it is quite convenient, it allows a faster web browsing as it doesn't have to request for DNS at each connection to recently visited websites.
This could be very troublesome when you wish to set up manually the IP address of a server (e.g. to test purposes via the host file).
To disable the DNS cache:
From your browser:
Type in
about:config in the address bar.
Right click on the list of
Properties, select
New > Integer in the
Context menu
Enter
network.dnsCacheExpiration as the preference name and
0 as the integer value
When disabled, Firefox will use the DNS cache provided by the OS.