Performance and connectivity
Deal with error messages, crashing applications, connectivity issues, and slow performance.
Secure connection failed and Firefox did not connect
If a website requires a secure connection that cannot be established, Firefox will not connect and will show you an error page. Learn more.
Last updated:
How to troubleshoot time related errors on secure websites
Learn why you might see time-related errors on HTTPS websites and how you can troubleshoot these errors by correcting your system clock.
Last updated:
Website will not allow Firefox to display the page if another site has embedded it
This page explains the error: "Website will not allow Firefox to display the page if another site has embedded it"
Last updated:
Captive portal detection
Description of how Firefox detects captive portal networks.
Last updated:
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.
Last updated:
Fix "The bookmarks and history system will not be functional" error message
This article explains what to do if you see the error message “The bookmarks and history system will not be functional” when you start Firefox.
Last updated:
How to troubleshoot security error codes on secure websites
Learn about error code SEC_ERROR_UNKNOWN_ISSUER MOZILLA_PKIX_ERROR_MITM_DETECTED and ERROR_SELF_SIGNED_CERT on secure sites and how to troubleshoot.
Last updated:
Diagnose Firefox issues using Troubleshoot Mode
Use Firefox Troubleshoot Mode (known as Safe Mode in previous versions of Firefox) to diagnose and fix problems. Learn more.
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.
Last updated:
Troubleshoot and diagnose Firefox problems
This article includes a series of steps you can follow, that will help you fix most problems with Firefox.
Last updated:
Firefox uses too much memory or CPU resources - How to fix
Learn how to reduce Firefox's system resource usage for a faster, more stable browsing experience.
Last updated:
Warning Unresponsive script - What it means and how to fix it
This article describes the reasons for this error message and covers possible solutions and workarounds.
Last updated:
Resist Fingerprinting
Firefox's Advanced Preferences to resist fingerprinting can help prevent websites from uniquely identifying your device but can cause problems. Learn more.
Last updated:
Task Manager - see whether tabs or extensions are slowing down Firefox
Firefox has a feature that lets you see how much memory and CPU resources are being used by tabs, extensions and other processes. Learn more.
Last updated:
How to let Firefox use the internet on your Windows computer
A "Server not found" error can be caused by Windows Firewall blocking Firefox from accessing the Internet. Learn how to configure it to allow Firefox access.
Last updated:
Use the Troubleshooting Information page to help fix Firefox issues
The Troubleshooting Information page has tools and details about your Firefox installation, that can help you solve problems with Firefox.
Last updated:
Firefox hangs or is not responding - How to fix
When Firefox hangs, it stops responding to clicks or keystrokes and seems to be frozen. This article has possible solutions, depending on when this happens.
Last updated:
"Firefox is already running but is not responding" error - How to fix
How to start Firefox if you see an error message, "Firefox is already running, but is not responding" or, on macOS, "A copy of Firefox is already open".
Last updated:
How do I report a broken site in Firefox desktop?
How to report a broken website and what information Mozilla receives when you report breakage caused by Enhanced Tracking Protection.
Last updated:
Firefox can't load websites but other browsers can
We'll explain errors such as "Server not found" or "Unable to connect" and how to fix problems where Firefox can't access websites but other browsers can.
Last updated:
How to fix the Update Failed error message when updating Firefox
This article presents solutions and workarounds to a failed Firefox update so that you can get it updated and working correctly again.
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.
Last updated:
Unload inactive tabs to save system memory in Firefox
Learn how to free up system memory by unloading inactive tabs in Firefox.
Last updated:
Certificate contains the same serial number as another certificate
Why Firefox may show you a Secure Connection Failed error when you try to access the configuration page for your router and what to do.
Last updated:
How to reset the default user agent on Firefox
Learn how to reset your Firefox "user agent" so that websites can detect your correct browser and version and work the way they should.
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.
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.
Last updated:
Quick fixes if your Firefox slows down
The article covers the steps you can take to make Firefox run faster.
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.
Last updated:
Firefox blocked by macOS 15 Sequoia firewall - What you need to know
Some macOS 15 users may have Firefox blocked by the firewall. Learn about the issue and how to help Mozilla investigate.
Last updated:
Firefox says it's just updated every time it starts - how to fix
If you see "Firefox Updated" or "You've been updated to the latest version of Firefox" every time you start Firefox, we'll show you how to fix it.
Last updated:
Firefox does not work - Common fixes to get you back up and running
Find solutions to Firefox issues like crashing, not starting, slowness and websites not loading.
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.
Last updated:
Server Not Found - Troubleshoot connection problems
If you can't connect to a website, you may see the Server Not Found error message. Learn how to troubleshoot and fix this error.
Last updated:
Rate your Firefox experience, surveys and out of date messages (Heartbeat)
You may be selected to rate Firefox or complete a survey. You may also see a notice to update Firefox. Learn more about these messages.
Last updated:
Drag and Drop errors with Firefox Launcher Process enabled and Windows UAC disabled - How to Fix
How to fix Firefox drag-and-drop errors when running Windows as Administrator with UAC disabled and the Launcher Process enabled.
Last updated:
Solutions for "Can not create temp folder archive" error when installing Firefox (Windows 10)
Stuck with the "Can not create temp folder archive" error on 7-Zip when installing Firefox for Windows 10? This article will help you to solve the issue.
Created:
Websites look wrong or appear differently than they should
This article explains how to fix problems with websites that display incorrectly in Firefox or don't work the way they should.
Last updated:
2 weeks, 3 days ago
Firefox takes a long time to start up
This article describes some causes of a long start up time and steps you can take to improve it.
Last updated:
Firefox uses too many CPU resources - How to fix
At times, Firefox may require significant CPU resources to display content. We'll show you options for fixing this if this if it is happening too often.
Last updated:
Websites say that Firefox is outdated or incompatible even though it's the latest version
Some websites that need a specific browser or version make a mistake detecting your installed version of Firefox. We'll explain how to fix or work around this.
Last updated:
Memory constraints, Firefox performance and Firewalls
Firefox's performance can be adversely effected by memory constraint issues. Learn how to identify memory constraint problems and solutions.
Last updated:
How to resolve weak crypto error messages on Firefox
When connecting to a website that uses an invalid TLS certificate or weak encryption, Firefox will display an error page saying "Your connection is not secure".
Created:
64-bit Firefox crashes with Citrix's XenApp VM
The API hooks from Citrix XenApp 7.13 VDA do not work with 64-bit Firefox. How to find a workaround.
Last updated:
How to fix an error when trying to open Telegram or Slack on Firefox
How to fix the NS_ERROR_DOM_ABORT_ERR while trying to open web.telegram.org or app.slack.com on Firefox 87 or above.
Last updated:
Identify problems caused by third-party modules in Firefox for Windows
Identify problems caused by third-party modules in Firefox for Windows.
Last updated:
Difficulties opening or using a website in Firefox 100
A potential temporary solution if a web page is not opening correctly in Firefox 100.
Last updated:
Firefox hangs when copying with Suggested Actions enabled on Windows 11 - What to do
Firefox can freeze or stop responding when copying, with the Suggested Actions feature enabled on Windows 11. Learn how to fix the problem.
Last updated:
X-Mouse Button Control in Firefox 110
Learn about an issue with X-Mouse Button Control in Firefox 110 for Windows.
Last updated:
Address screen sharing issues with Firefox on macOS 15 Sequoia
Learn how to resolve screen sharing issues in Firefox when using macOS 15 'Sequoia' due to changes in Apple's API.
Last updated:
Troubleshoot Firefox crashes (closing or quitting unexpectedly)
Learn how to troubleshoot and fix Firefox crashes, and find out how to get more help if you're having problems solving the issue.
Last updated:
Firefox repeatedly opens empty tabs or windows after you click on a link
Firefox may repeatedly open empty tabs or windows after you click on a link, forcing you to close Firefox. Learn how to fix this problem.
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.
Last updated:
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.
Last updated:
Fix video and audio problems on Firefox for Windows N editions
If Firefox has trouble playing video or music on a Windows computer, you can install the Media Feature Pack, if it's missing. Learn more.
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.
Last updated:
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.
Last updated:
Home page with pipe character opens extra tabs when Firefox starts
Set up Firefox to open multiple home pages replacing the pipe character (|) with %7C.
Last updated:
How to run Firefox when your profile is missing or inaccessible
How to fix the error ''Your Firefox profile cannot be loaded. It may be missing or inaccessible'' so that you can start and run Firefox.
Last updated:
