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.

Firefox Firefox Last updated:

Mozilla Crash Reporter TB

The Mozilla Crash Reporter dialog box appears when Thunderbird crashes and lets you send a crash report. Learn how it works and how to access your crash reports.

Thunderbird Thunderbird Last updated:

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.

Firefox Firefox Last updated:

Rebuilding the Global Database

Rebuilding the Global Database will initiate a re-indexing of emails and address book cards (newsgroup messages are not indexed).

Thunderbird Thunderbird Last updated:

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.

Firefox Firefox Last updated:

Troubleshoot Mode Thunderbird

How to use Thunderbird's Troubleshoot Mode to find and fix problems, especially if they are caused by add-ons.

Thunderbird Thunderbird Last updated:

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.

Firefox Firefox Last updated:

How can I tell if Mozilla VPN is connected?

Mozilla VPN displays visual indicators of its current status, making it easy to know whether your online activity is protected or not.

Mozilla VPN Mozilla VPN Last updated:

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.

Firefox, Firefox for Android Firefox, Firefox for Android Last updated:

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.

Firefox, Mozilla Account Firefox, Mozilla Account Last updated:

How to enable Always-on VPN on Android

Enable “Always-on VPN” on Android to encrypt your connection automatically every time you browse the Internet on your phone.

Mozilla VPN Mozilla VPN Last updated:

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.

Firefox Firefox Last updated: 2 weeks, 5 days ago

Some videos won't play in background

Some popular video websites have changed their settings on the server side so that videos will no longer play in the background.

Firefox for Android Firefox for Android Last updated:

Thunderbird makes unrequested connections

Thunderbird sometimes automatically connects to the Internet. These connections are for routine maintenance, update and security purposes.

Thunderbird Thunderbird Last updated:

How to obtain the Mozilla VPN Logs

When troubleshooting issues with Mozilla VPN, our engineers can ask for logs. These don't contain any personal information, but give hints about the issue.

Mozilla VPN Mozilla VPN Last updated:

Firefox for iOS won't load web pages

If a website isn’t loading even after you’ve checked the Internet connection, here are a few things you can try.

Firefox for iOS Firefox for iOS Last updated:

How do I contact MDN Plus support?

Learn how to contact support if you can’t find the answer to your question in the MDN Plus support knowledge base.

MDN Plus MDN Plus Last updated:

RCS messaging and Mozilla VPN

RCS (Rich Communication Services) messaging on iOS 18 does not work when using Mozilla VPN. Learn how to fix or work around this issue.

Mozilla VPN Mozilla VPN Last updated:

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.

Firefox Firefox Last updated:

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.

Firefox Firefox Last updated:
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