Connections established on startup - Firefox

The following is a list of all connections that Firefox may establish at application startup and how to stop them.

A loopback connection (to IP address 127.0.0.1) on non-Unix machines [1]. The browser is communicating normally with itself, and it is not recommended this be blocked.
Loading Live Bookmarks. Deleting all Live Bookmarks will stop these connections.
Checking for application updates. "Tools -> Options -> Advanced -> Update" provides options to disable update checks.
Loading home page. Setting the homepage to a blank page or a local page will stop this connection.
Updating phishing sites database. Setting browser.safebrowsing.enabled to false in about:config will disable this feature.
Prefetching links if the page it's on defines any. See the Prefetch FAQ and network.prefetch-next for further information. To disable pings in prefetched links, see browser.send_pings.
Updating the Add-ons Blocklist. Setting extensions.blocklist.enabled to false in about:config will disable this feature.
Updating metadata for installed add-ons (described here). Setting extensions.getAddons.cache.enabled to false in about:config will disable this feature. [2]
Firefox Health Report data. [3]

External links