Some people are concerned about the connections Firefox makes to the Internet, especially when those connections are made for no apparent reason (see Mozilla's Firefox Browser Privacy Notice for additional information). This article explains various reasons why Firefox may make a connection to the Internet and how you can stop it from doing so, if you wish.

Automatic updates and Security

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. Check Never check for updates (not recommended: security risk) and uncheck Search Engines.

Blocklist updating

Firefox may be updating its blocklist, which is used to block malicious extensions, vulnerable plugins, revoked certificates and graphics drivers known to cause crashes. For more information, see Blocklisting (MozillaWiki), Blocklisting/Graphics (MozillaWiki), the Revoking Intermediate Certificates: Introducing OneCRL blog post 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.

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.

Secure website certificates

When you visit a secure website (i.e. "https"), Firefox will validate the website's certificate. This may involve communicating with a third-party status provider specified by the certificate over a protocol namend OCSP to confirm that the certificate is still valid. 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 Advanced panel.
3. Select the Certificates tab.
4. Uncheck Query OCSP responder servers to confirm the current validity of certificates.

Prefetching

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 Link 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.

DNS prefetching

In order to reduce latency, Firefox will proactively perform domain name resolution on links that the user may choose to follow as well as URLs for items referenced by elements in a website. For more information, please see the DNS Prefetching blog post. To disable DNS 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.dns.disablePrefetch.
3. Observe the Value column of the network.dns.disablePrefetch row.
   • If it is set to true then do nothing.
   • If it is set to false, double-click on it to set it to true.

Speculative pre-connections

To improve the loading speed, Firefox will open predicitive connections to sites when the user hovers their mouse over thumbnails on the New Tab Page or the user starts to search in the Search Bar, or in the search field on the Home or the New Tab Page. In case the user follows through with the action, the site can begin loading faster since some of the work was already started in advance. 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 network.http.speculative-parallel-limit.
3. Observe the Value column of the network.http.speculative-parallel-limit row.
   • If it is set to 0 then do nothing.
   • If it is set to a different value, double-click on it to set it to 0.

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.

User-invoked content

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.

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.

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.

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.

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

Search plugin icon loading

When you add a custom search plugin that doesn't come with an included icon, Firefox might look up the icon at a remote address that is specified in the search plugin once and cache it for future use.

Firefox Sync

If you're using Firefox Sync, it will establish regular connections in order to synchronize your data to Mozilla's sync servers and across your connected devices. In order to choose what data gets synchronized or to disconnect from sync, see the How do I choose what information to sync on Firefox? article.

Mozilla content

Snippets

If you use the built-in default homepage about:home, Firefox will show some Mozilla related content around the search box ("Snippets"), which is updated once a day. If you'd like to disable connections to Mozilla's snippets server:

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 browser.aboutHomeSnippets.updateUrl.
3. Double-click on it and set its value to a blank string.

"What's new" page

After a browser update, Firefox might show an additional tab next to your usual homepage to offer more information on changes or new features included in the update. To disable this page from being shown:

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 browser.startup.homepage_override.mstone.
3. Double-click on it and set its value to ignore.

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.

Diagnostics

Firefox can submit certain diagnostics data including Telemetry, Firefox Health Report and Crash Reports to Mozilla to provide information that helps improving the browser. In order to disable the sharing of this data, refer to Data Choices Tab.

Media capabilities

WebRTC

WebRTC (Web Real-Time Communication) is a technology which provides direct browser-to-browser communication (audio, video, filesharing). As it is drafted and implemented at the moment, WebRTC can lead to your local IP address being exposed to websites even when you are behind a VPN or a NAT router - in the WebRTC API this data would be used to set up a peer-to-peer connection between to clients. There is discussion about if and how this should be adressed at the moment. If you would like to disable WebRTC:

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 media.peerconnection.enabled.
3. Observe the Value column of the media.peerconnection.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.

Malware

If your computer is infected with a virus, trojan, spyware, or other malicious software, then Firefox's Internet connection may be being piggybacked in order for the malware to communicate with its author or to deliver advertisements, etc. If you suspect this is the case, consider seeking advice from a forum specializing in malware removal. For more information, see Troubleshoot Firefox issues caused by malware.

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.

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