If you are monitoring your Internet connection activity, you may notice that Thunderbird sometimes automatically connects to the Internet. These connections are for routine maintenance, update and security purposes, which are described on this page.

Loopback connection

Thunderbird makes a "loopback" connection to IP address 127.0.0.1 on non-Unix machines. That IP address is the local address of the machine where Thunderbird is running. This connection is not a security problem and should not be disabled. See the Firefox bug 100154 for more information.

Auto-update checking

Thunderbird periodically checks to see if updates are available for itself or for installed add-ons (extensions, themes, etc). To disable these checks:

1. In the menu bar, click the Thunderbird menu and select Settings.Click the menu button and choose Settings.
2. Select the Advanced panel.
3. Select the Update tab.
4. Uncheck the Thunderbird and Installed Add-ons options.Check Never check for updates (not recommended: security risk).

Home page loading

By default, Thunderbird automatically loads a page with the latest Thunderbird information when the application is started. This page is downloaded from the Internet. To prevent Thunderbird from loading this page:

1. In the menu bar, click the Thunderbird menu and select Settings.Click the menu button and choose Settings.
2. Select the General panel.
3. Uncheck the When Thunderbird launches, show the Start Page in the message area option.

Add-on list prefetching

Each time the Add-ons tab is opened, Thunderbird prefetches a list of add-ons to improve responsiveness of the Get Add-ons pane. This connection is only made when the Add-ons Manager is opened.

Extension blocklist updating

Mozilla maintains a list of extensions that are not approved for use with Thunderbird. Thunderbird downloads this list from the Internet. To disable this:

1. In the menu bar, click the Thunderbird menu and select Settings.Click the menu button and choose Settings.
2. Select the Advanced panel.
3. Select the General tab.
4. Click Config Editor….
5. Enter extensions.blocklist.enabled in the Search field.
6. Observe the Value column of the extensions.blocklist.enabled row.
   • If it is set to false, then do nothing.
   • If it is set to true, double-click on it to set it to false.

Extensions

Installed and activated extensions may connect to the Internet. For example, a translation extension might connect to the Internet to look up words in a dictionary. See the Add-ons and Extensions FAQ for information about disabling add-ons.