Firefox: No connection to localhost domains when offline

After upgrading from Ubuntu 14.04 to Ubuntu 16.04, I was not able to connect to domains pointing to 127.0.0.1 when I had no network connection - in Firefox. In Chrome, it worked correctly. ​

As a web developer, I have a bunch of projects running on my laptop with domain names defined in /etc/hosts that point to the local machine, 127.0.0.1. On the train I have no internet connection but still want to work on my projects, so it's crucial to be able to access them. ​

Symptom​

When accessing http://www.bogo/ that has an entry in /etc/hosts, Firefox showed an error page: ​

Seite wurde nicht gefunden ​

Die Verbindung mit dem Server www.bogo.com schlug fehl.
Falls die Adresse korrekt ist, können Sie noch Folgendes versuchen: ​

  • Die Seite später noch einmal aufrufen.​
  • Die Netzwerkverbindung überprüfen.​
  • Falls der Computer sich hinter einer Firewall befindet, überprüfen Sie bitte, ob Firefox der Internetzugriff erlaubt wurde. ​
​

In english: ​

Hmm. We’re having trouble finding that site. ​

We can’t connect to the server at www.bogo.com.
If that address is correct, here are three other things you can try: ​

  • Try again later.​
  • Check your network connection.​
  • If you are connected but behind a firewall, check that Firefox has permission to access the Web. ​
​

Solution​

I found question that had the correct solution for me: ​

  1. Open about:config​
  2. Search for network.dns.disableIPv6​
  3. Set it to false​

After that it worked for me. ​

Firefox bug 1267257 seems to be describing this issue. ​

Written by Christian Weiske.

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