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. 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. See Managing Firefox Updates.

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, uncheck Update Add-ons Automatically and then select Reset All Add-ons to Update Manually.

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 Add-ons Blocking Process (Firefox Extension Workshop), Blocklisting/Graphics (MozillaWiki), Revoking Intermediate Certificates: Introducing OneCRL (Mozilla Security Blog) and the Add-ons that cause stability or security issues are put on a blocklist article. 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 it to set it to false.

Anti-phishing and malware protection lists updating

Phishing, unwanted software and malware protection lists may be updating. 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 Privacy & Security panel.
3. Uncheck Block dangerous and deceptive content.

In addition, when you download an application file, Firefox will verify its signature. If it is signed, Firefox then compares the signature with a list of known safe publishers. For files that are not identified by the lists as “safe” (allowed) or as “malware” (blocked), Firefox asks Google’s Safe Browsing service if the software is safe by sending it some of the download’s metadata. To turn off this part of malware protection:

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.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 it to set it to false.

Tracking protection list updating

The tracking 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 Privacy & Security panel.
3. Under Enhanced Tracking Protection, choose the Custom setting.
4. Uncheck Tracking content.

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 named 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 Privacy & Security panel.
3. In the Security section under Certificates, uncheck Query OCSP responder servers to confirm the current validity of certificates.

Login breach information

Firefox Monitor warns you if your online accounts were involved in a known data breach. For more information, see Firefox Password Manager - Alerts for breached websites.

To get the latest login breach information and more, Firefox connects to firefox.settings.services.mozilla.com

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 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 web page. 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 it to set it to true.

Speculative pre-connections

To improve the loading speed, Firefox will open predictive 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 page 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 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 Recommendations panel. This connection is not made if the add-ons manager is not opened.

User-invoked content

Home page loading

To set 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 Home panel.
3. Under New Windows and Tabs:
   • in the drop-down menu after Homepage and new windows, select Blank Page.
   • in the drop-down menu after New tabs, select Blank Page.
4. Close the about:preferences page.

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 disable or remove your extensions, see Disable or remove Add-ons.

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 How do I choose what information to sync on Firefox?

Mozilla content

Contextual feature recommendations and other notifications

Firefox may make feature recommendations specific to a type of website you're on or relevant to a current task. You can disable connections by opting out of all Firefox recommendations via Firefox settings. See Recommendations from Firefox for details.

Experiments or studies

• To disable new feature experiments, set messaging-system.rsexperimentloader.enabled to false.
• To disable the running of experiments, set app.shield.optoutstudies.enabled to false. This is not necessary if app.normandy.enable is also set to false.
• To disable studies, feature rollouts and emergency hotfixes related to Normandy, set app.normandy.enabled to false.

Geolocation for default search engine

In order to set the right default search engine for your location, Firefox will perform a geolocation lookup once by contacting Mozilla's servers and store the country-level result locally. This connection happens on the first start of Firefox – in case you want to prohibit that, you will have to preconfigure the browser and set the browser.search.geoip.url preference 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 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 Recommendations panel. 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 it to set it to false.

Diagnostics

Firefox can submit certain diagnostics data, including Telemetry and Crash Reports data to Mozilla, to provide information that helps improve the browser. You can disable sharing of this data in Firefox Settings . To disable the sharing of this data:

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 Privacy & Security panel.
3. Uncheck the boxes under the section Firefox Data Collection and Use.

In addition, Mozilla will ask a small sample of users to rate their experience with Firefox to get a better insight into the sentiment about the browser. For more information about this, see Firefox/Shield/Heartbeat (MozillaWiki). The rating feature will establish a connection to Mozilla's servers at startup, which you can turn off like this:

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. Find the preference app.normandy.enabled.
3. Set the preference value to false by double-clicking it.

Media capabilities

OpenH264 codec

Firefox will make use of the OpenH264 codec provided by Cisco in order to support the H.264 video codec in WebRTC, a technology allowing for peer-to-peer video communication on the web. For more information about this, see the OpenH264 Now in Firefox blog post.

The OpenH264 codec is not distributed with Firefox but gets downloaded at the first start of Firefox. In case you want to prohibit that, you will have to preconfigure the browser and set the media.gmp-gmpopenh264.enabled preference to false.

DRM content

To disable this feature, see Watch DRM content on Firefox.

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 two local clients.

For different methods and granular controls on how to mitigate this issue, see Media/WebRTC/Privacy Media/WebRTC/Privacy Media/WebRTC/Privacy Mozilla Wiki page.

Network Detection

Firefox's captive portal feature tests whether your network connection requires logging in, for example, on a public Wi-Fi hotspot, by regularly connecting to https://detectportal.firefox.com/success.txt. Firefox will also make connections to this URL to check if your current network supports IPv6.

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.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 it to set it to false.
4. In the about:config page, search for the preference network.connectivity-service.enabled (for example, you can type connectivity in the search box above the list and pause while the list is filtered).
5. Observe the Value column of the network.connectivity-service.enabled row.
   • If it is set to false then do nothing.
   • If it is set to true, double-click 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)