Performance and connectivity

Deal with error messages, crashing applications, connectivity issues, and slow performance.

Connection settings in Firefox

Your organization or Internet Service Provider may offer or require you to use a proxy to connect to the Internet. Learn more.

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What do the security warning codes mean?

Firefox shows you a warning page about a potential security risk when you try to connect to a secure site but your connection is not secure.

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DNS over HTTPS (DoH) FAQs

We have outlined a list of FAQs here that you may find helpful while getting up to speed with all that DNS over HTTPS (DoH) has to offer.

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Resist Fingerprinting

Firefox's Advanced Preferences to resist fingerprinting can help prevent websites from uniquely identifying your device but can cause problems. Learn more.

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Firefox DNS over HTTPS

DoH improves privacy by hiding domain name lookups from anyone lurking on public Wi-Fi, your ISP or others on your local network. Learn more.

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Where to go for developer support

Have questions about web development or Firefox Developer Edition? MDN Web Docs has many resources you'll need to build a better web. Learn more.

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Disable Firefox Sync

Learn how to turn off Firefox Sync if you’d like to use your Mozilla account without syncing data such as, bookmarks, history and tabs.

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HTTPS-First upgrades to secure connections

From version 136, Firefox implements HTTPS-First and always attempts to connect securely. If a secure connection fails it falls back to an insecure connection.

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Firefox is stuck in Troubleshoot Mode

Learn why Firefox may start in Troubleshoot Mode (previously known as "Safe Mode") when you expect it to start normally and how to fix it.

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Avoid crashes - Tips and tricks

Here are some easy things you can do to avoid crashes and keep Firefox running in tip-top shape.

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Firefox keeps crashing at startup

If Firefox keeps crashing when you try to start it and other solutions don't work, a clean reinstall can often fix the problem.

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Problems with email and how to find help

Find out the right direction to get help using webmail in Firefox and links to support pages for popular web-based email services.

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