How to flush DNS cache in Firefox

Question

Strange issue... whenever I try to access http://docs.python.org/ from Firefox on Win 7, I get redirected to http://docs.python.org/old_dns.txt which says:

You need to update your DNS records for docs.python.org. This is the old docs server.

My first thought was to do a ipconfig /flushdns, but that didn't fix the problem.

I also determined that the it wasn't a cache at my local network nor ISP level... (both returns 199.27.76.175)

C:\>nslookup docs.python.org.
Server:  [INSTITUTION AD DNS SERVER - REMOVED]
Address:  [REMOVED]

Non-authoritative answer:
Name:    c.global-ssl.fastly.net
Address:  199.27.76.175
Aliases:  docs.python.org


C:\>nslookup docs.python.org. 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
Name:    c.global-ssl.fastly.net
Address:  199.27.76.175
Aliases:  docs.python.org

I have the Flagfox extension installed and it's showing 199.27.76.175 as the address as well.

Ctrl-F5 to refresh did not work either.

The weirdest thing is when I accessed the same address in Chrome, it worked (redirected me to https://docs.python.org/3/)

Having known this, I tried https://docs.python.org/ (notice the httpS) in Firefox, and it worked as well! (Redirected to https://docs.python.org/3/).

What's up with this?! How can I fix this?

Since Chrome works and the IP is obviously the same as Google's DNS server, I assume this is caused by a Firefox internal DNS cache and the Flagfox address displayed is resolved separately and not the actual address used to contact the server.

Solution 1

I have learned that you must press Control+F5 a few times on Firefox for it to have any effect.

Btw there's also a DNS Flusher addon.

Solution 2

Are you (or your company) perhaps using a proxy that might have cached the DNS record? Even though you have flushed your local DNS cache, the proxy might need to flush it's DNS cache too.

Comments

[MaQleod]

You can modify how firefox caches using about:config and the network.dnsCacheExpiration key. Setting it to 0 disables cache altogether. If you wait longer than the value in seconds specified in that key, the query will not use a cached result from firefox (kb.mozillazine.org/Network.dnsCacheExpiration)