Some people are particularly concerned about the connections Firefox makes to the Internet, especially when such connections are made with no apparent cause. This article will explain the various reasons why Firefox may make a connection to the Internet, and how you can stop it from doing so if you so desire.

Loopback connection

A loopback connection (to IP address 127.0.0.1) can be made by Firefox on non-Unix machines. In this case the browser is communicating with itself as expected, and it is not recommended that this communication be blocked. See bug 100154 for more information.

Live Bookmarks updating

Live Bookmarks - Subscribe to a web page for news and updates automatically reload themselves on a regular basis, and in doing so will make a connection to the Internet. Deleting all your Live Bookmarks will stop these connections from being made.

Auto-update checking

Firefox occasionally checks to see if any updates are available for itself and for your search engines. To disable these checks:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the Advanced icon.
3. Select the Update tab.
4. Uncheck Automatically check for updates to: and Search Engines.Check Never check for updates (not recommended: security risk) and uncheck Search Engines.

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

1. Click the menu button , click Add-ons and themes and select Extensions.
2. At the top of the tab, click the Tools for All Add-ons menu and uncheck Update Add-ons Automatically, then select Reset All Add-ons to Update Automatically.

Home page loading

Your home page may be loading. To change your home page to something that doesn't generate connections to the Internet:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the General panel.
3. Either set When Firefox starts to Show a blank page or set it to Show my home page and click Restore to Default.

Anti-phishing list updating

The phishing protection list may be updating itself. To turn this off:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the Security panel.
3. Uncheck Block reported web forgeries.

Anti-malware list updating

The malware protection list may be updating itself. To turn this off:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the Security panel.
3. Uncheck Block reported attack sites.

Add-on list prefetching

Each time the Add-ons manager is opened, Firefox prefetches a list of add-ons to improve responsiveness of the Get Add-ons pane. This connection is not made if the add-ons manager is not opened.

Blocklist updating

Firefox may be updating its blocklist, which is used to block malicious extensions, vulnerable plugins, and graphics drivers known to cause crashes. For more information, see Blocklisting (MozillaWiki), Blocklisting/Graphics (MozillaWiki) and the article Add-ons that cause stability or security issues are put on a blocklist. To disable this feature:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go 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.

Add-on metadata updating

The Add-ons manager displays information about each add-on you have installed and provides personalized recommendations in the Get Add-ons pane. To keep this data updated, Firefox will request information from the Mozilla Add-ons gallery once a day (for more information, see this blog post). To disable these updates:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. In the about:config page, search for the preference extensions.getAddons.cache.enabled.
3. Observe the Value column of the extensions.getAddons.cache.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.

Link prefetching

Firefox will prefetch certain links if any of the websites you are viewing uses the special prefetch-link tag. For more information, please see the Link Prefetching FAQ. To disable prefetching:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. In the about:config page, search for the preference network.prefetch-next.
3. Observe the Value column of the network.prefetch-next 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

An extension you have installed may be making a connection to a website that it relies on. For example, a connection to a website to synchronize your bookmarks, a connection to a website to update a list of sites to block, etc. Or it is possible an extension could be changing the expected behavior of Firefox in other ways. For example, FasterFox extension has an option to prefetch all links.

To easily disable all of your extensions please read the Diagnose Firefox issues using Troubleshoot Mode article, paying particular attention to the Disable all add-ons option under the Make Changes and Restart section. To disable or remove your extensions, see the Disable or remove Add-ons article.

Downloads restarted

When you start Firefox, any interrupted downloads from your previous browsing session may be automatically resumed.

1. Press Ctrl + JCtrl + Shift + Ycommand + J to open the Downloads window.
2. Ensure nothing is currently being downloaded

Based on information from Connections established on startup - Firefox (mozillaZine KB)