Stop Firefox from making automatic connections.

Some people are concerned about the connections Firefox makes to the Internet, especially when those connections are made for no apparent reason. This Post explains various reasons why Firefox may make a connection to the Internet and how you can stop it from doing so, if you wish.

Firefox occasionally checks to see if any updates are available for itself and for your search engines. The ability to disable Firefox update checking was removed in Firefox 63. Advanced users and IT administrators can use a policy to disable Firefox update checks.

Firefox also checks to see if any updates are available for your add-ons (extensions, themes). 

1. How Can i Disable Automatic updates?
To disable this feature:

1. In the address bar, type about:config and press Enter Key.
   A warning page may appear. Click Accept the Risk and Continue to continue to the about:config page.
2. In the about:config page, search for the preference extensions.blocklist.enabled
3. 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.

2. Disabling Anti-phishing and malware protection?
To disable this feature:

1. In the address bar, type about:config and press Return.
   A warning page may appear. Click Accept the Risk and Continue to continue to the about:config page.
2. In the about:config page, search for the preference browser.safebrowsing.downloads.remote.enabled
3. Observe the Value Column of the browser.safebrowsing.downloads.remote.enabled row.
   • If it is set to false then do nothing.
   • If it is set to true then double-click on it to set it to false.

3. Disable Network Detection Requests.
To Disable This Feature:

1. In the address bar, type about:config and press Return.
   A warning page may appear. Click Accept the Risk and Continue to continue to the about:config page.
2. In the about:config page, search for the preference network.captive-portal-service.enabled (for example, you can type portal in the search box above the list and pause while the list is filtered).
3. Observe the Value column of the network.captive-portal-service.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.

For Detailed information See Firefox Documentation: https://support.mozilla.org/en-US/kb/how-stop-firefox-making-automatic-connections