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Firefox was created by Dave Hyatt and Blake Ross as an experimental branch of the Mozilla browser, first released as Firefox 1.0 on November 9, 2004. Starting with version 5.0, a rapid release cycle was put into effect, resulting in a new major version release every six weeks. Quit Firefox: Click the Firefox menu and select Exit. Click the Firefox menu at the top of the screen and select Quit Firefox. Click the Firefox menu and select Quit. Uninstall Firefox - If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux for details.

Mozilla's Firefox browser is known for its speed and a large collection of extensions that let you customize the experience to your heart's desire. But when Firefox is running slow, crashing, or not loading websites properly, it can be frustrating to figure out why. Follow our step-by-step guide to get your Firefox back to tip-top condition.

What are the most frequent problems with Firefox?

Computer users who have problems with 'virus alert from microsoft' virus removal can reset their Mozilla Firefox settings. Open Mozilla Firefox, at the top right corner of the main window, click the Firefox menu, in the opened menu, click Help. Select Troubleshooting Information. In the opened window, click the Refresh Firefox button. If Firefox previously worked but stopped after you installed extensions or themes, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems. Firefox previously worked. If Firefox previously worked but suddenly doesn't start, it may be due to some corrupt data in your settings.

Overall, Firefox is a top-rated and highly reliable browser — good choice for both professional and everyday users. However, serving so many platforms on so many devices and screens, even the best of the best sometimes let us down. But worry not, in this how-to we've combined the most frequently occurring Firefox problems and written specific instructions on how to fix them.

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Why is Firefox so slow, hangs or keeps freezing?

Slow Firefox browsing experience is truthfully beyond annoying. It seems like it's almost working, but you can't get anything done.

Here we've listed some suggestions that should get your Firefox run faster.

1. Close inactive tabs

See how many tabs you have opened. More than a few? Active tabs mean active processes that take up your laptop's RAM and drastically slow down its capabilities. Just close the tabs you're not actively using. If they are important to remember, save them to bookmarks or stash them in a special 'Read Later' list in a to-do application such as 2Do.

2. Clear Firefox cookies and cache

All the websites you visit leave behind cached image files, which are supposed to speed up load times, and cookies, which can save you from having to log in over and over. Those are big conveniences if they work the way they're supposed to, but sometimes cache and cookies can cause glitches and slowdowns.

If Firefox is acting up, you can clear cookies and cache by doing the following:

• Click the Library button
• Choose History > Clear Recent History
• Change the time range to Everything
• Click the arrow next to the word Details
• Select Cache and Cookies
• Then click the Clear Now button

Alternatively, you can do this easier and safer with CleanMyMac. Just click Privacy in the sidebar and then choose Firefox from the list. Change the time range to Everything, and you can clear all of the cookies, browsing history, downloads history, tabs, saved passwords, and even autofill values.

3. Update Firefox and macOS

If closing tabs and clearing the cache didn't work, it's a good idea to update Firefox and macOS to its latest versions. When Firefox is active, just click on Firefox in the menu and select About Firefox. The latest available update should start downloading automatically. When it's ready, click Restart to Update Firefox and you are ready to go.

Updating macOS is easy too. Just launch the App Store on your Mac. Go to the Updates tab and wait till it shows you all the new software versions available. If you see new updates for macOS, click Update and follow the restart instructions.

4. See what consumes hardware resources

If the problem persists, check for high hardware resource usage. For basic information, you can use Mac's native Activity Monitor. However, to see the whole picture, get a pro-level app, such as iStat Menus. If you see Firefox using too much memory or CPU, you need to take some action.

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5. Troubleshoot plugins and extensions

When Firefox stops responding to your clicks it's very likely that one of your installed plugins is the culprit. To check for that, click the Menu button, and then choose Add-ons. In the Add-ons Manager's Plugins panel, you can select Never Activate for each plugin, then restart Firefox and see if the problem is still happening.

If the problem is gone, turn the plugins back on one by one, just changing that Never Activate option back to Always Activate. Restart Firefox each time and then try to recreate the error. Once the problem reappears, you'll know it was likely caused by the last plugin you re-enabled.

You can also remove a plugin with CleanMyMac's Extensions tab, which is actually a lot easier than using Firefox. In Firefox itself, you have to type about:plugins, then find the file path for that plugin and navigate to it in the Finder. Mozilla then recommends you change the filename to add an X in front, which will remove the plugin. You can reinstall a fresh copy of the plugin (from official sources only!), or just see if you can live without it.

To check your extensions in Firefox, go to about:add-ons, then click Extensions in the sidebar. You can disable extensions here, and then turn them back on one by one, in the same way you just checked your plugins. If you want to remove all your extensions and start fresh, you can click the Remove button or use the Extensions tab in CleanMyMac, which manages extensions, add-ons, and plugins from one place.

6. Stop loading Flash content

Preventing Flash content from loading automatically deserves a separate explanation. Some websites use way too much Flash content, and loading and playing all of that uses up your computer's resources, especially if you keep a lot of tabs open. Luckily, you can tell Firefox to stop loading Flash content by default, until you ask for it.

1. Click the Menu button and select Add-ons, or select Tools > Add-ons from your Mac's menu bar. (Or press Command-Shift-A, or type about:add-ons into the URL bar. It all takes you to the same place.)
2. In the Add-ons Manager, click Plugins in the sidebar, and then look for Shockwave Flash.
3. Change the dropdown from Always Activate to Ask to Activate. After that, websites will display an Activate Adobe Flash button in place of Flash content, and all you have to do is click that to allow Flash to display it.

Following the tips above should eliminate 90% of your Firefox problems. But if you're still experiencing troubles, there is more you can do. Read on.

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Mozilla Firefox crashes unexpectedly or won't open

Whether Firefox shows you an error message every time you try to launch the app or right when you're in the middle of a working session, there is only one way to fix that — reinstall the application.

The easiest way to reinstall Firefox is to quit it, delete the Firefox file from your Applications folder, and download the new version from the official Mozilla website. That will uninstall the application but keep all your user data intact, and when you reinstall a new copy, you bookmarks and passwords will still be there.

But that's not the best way to do it, since Firefox leaves all kinds of data on your hard drive besides the main application file. A better way is to use an application that's able to delete all Firefox information completely or simply reset the app, such as CleanMyMac.

To reset the Firefox browser app on mac:

1. Launch CleanMyMac
2. Go to the Uninstaller tab
3. Choose Firefox from the list
4. Choose Application reset and click Uninstall round button

There are rare cases when the 'Firefox quit unexpectedly' message could be caused by the Mac security update. This happens when your Mac's firewall used to recognize previous versions of Firefox but no longer trusts the new one. Follow official Mozilla documentation to fix this issue.

Firefox shows errors loading websites

So your Firefox is fast and doesn't randomly quit, but still doesn't seem to load websites. There are a few things that might cause this, so let's zero in on the problem by gradually excluding various perpetrators.

1. Check your network connection

Turn your modem off and on (helps in nearly all cases). Check that your network connection is performing up to standards by using WiFi analyzers, such as NetSpot and WiFi Explorer. As soon as you launch NetSpot, make sure it's set to Discover mode, and it will scan all nearby WiFi networks automatically. WiFi Explorer is just as easy — launch the app and click the play button to analyze the network quality around you.

2. Launch websites in other browsers

If your WiFi network seems to be fine, it's good to check whether the connection works in other browsers, like Safari or Chrome, just to make sure that the problem in fact is with Firefox specifically. Then, check the settings in your firewall by following the steps outlined by Mozilla.

3. Fix the proxy server issue

If upon loading the website you get the 'Proxy server is refusing connections' message, there is an easy fix for that.

1. Open Firefox > Menu > Options
2. In the Options, click Advanced and then Network
3. Choose Settings and then 'No proxy' and click OK
4. Restart Firefox and the problem should be fixed

4. Validate the security certificate

In case Firefox shows you that it has troubles validating some website's security certificate, it might be related to improperly set date and time on your system. Just make sure your timezone settings in System Preferences > Data & Time are configured correctly and Firefox should go back to validating the website certificate normally.

5. Flush DNS cache

Another option you can try is flushing the DNS cache, which acts as a temporary database, storing all sorts of connectivity logs and website access attempts.

1. Open up the Terminal utility
2. Type sudo killall -HUP mDNSResponder;say DNS cache has been flushed
3. Press Enter and type your admin password when prompted
4. An alert a few moments later will inform you that the process is complete

Combine flushing the DNS cache with clearing out cache and cookies from Firefox, and restarting your Mac to get the best result.

6. Disable DNS prefetching

If you are still experiencing troubles loading websites, it could be that DNS prefetching is at play. Usually Firefox tries to speed up loading new websites by using DNS prefetching, but it can also cause loading errors with some system configurations. To disable DNS prefetching:

1. In the address bar, type about:config and press Return. The about:config 'This might void your warranty!' warning page may appear. Click 'I accept the risk!' to continue.
2. Hold down the Ctrl key while you click on the list of preferences. Select New and then select Boolean.
3. In the 'Enter the preference name' field, enternetwork.dns.disablePrefetch and click OK.
4. Select True when prompted to set the value and click OK.

7. Scan your Mac for malware

The last step to try to fix the website loading issue is to check your system for malware. If you remember Firefox being haunted by ad pop-ups, toolbars you didn't install yourself, or a new default home page, you might have picked up some malware that's hijacking your browser sessions.

A simple malware tool for Setapp users is CleanMyMac Malware Removal tool. It's a free download, with a pro license for more active, real-time protection. The free product will however scan your Mac and safely remove any malware at no cost to you.

Firefox doesn't work as it should

When your Firefox is just generally behaving incorrectly, a few more tips might come in handy. Start with restarting your Mac, and then clear the cache and troubleshoot your plugins as described above.

1. Restart Firefox in Safe Mode

When clearing the cached data doesn't help, try restarting the browser in Safe Mode. This will temporarily turn off your extensions, as well as any extra themes and toolbars, and hardware acceleration. The easiest way to do this is to quit Firefox and restart it holding down your Mac's Option key.

If the problem you were having magically goes away in Safe Mode, then you can proceed to check your extensions, themes, and anything else you've added to Firefox. If you're still having the problem in Safe Mode, that's a sign you might need to just trash your copy of Firefox and start over with a fresh install.

2. Refresh Firefox

There is another clever feature inside Firefox that clears out your extensions and themes, plus resets all the preferences to default, but keeps your personal information intact, including bookmarks, history, open tabs and windows, saved passwords, autofill info, and even cookies.

• Open Firefox, and type about:support in the URL bar, which takes you to the Troubleshooting Information page
• You'll find a lot of information about your browser installation, as well as a big friendly Refresh Firefox button at the top-right
• You can also get to Safe Mode this way, by clicking the button that says Restart with Add-ons Disabled

3. Create a new Firefox profile

For times, when neither options fixed the problem, try creating a fresh Firefox profile, which won't have any of your bookmarks, passwords, and user preferences, but might get rid of the problem.

• Open the Terminal utility
• Type in /Applications/Firefox.app/Contents/MacOS/firefox-bin -P
• Press Enter and the Profile Manager window should open
• Click Create Profile… then Next and enter the name for the profile
• Press Done

4. Turn off hardware acceleration

In cases when Safe Mode seemed to fix the problem but checking plugins didn't bring any result, the problem may hide in hardware acceleration, which is off by default in Safe Mode. Here's how to turn it off in the regular mode too:

• Open Firefox > Preferences
• In the General panel, scroll down to the Performance section and uncheck the box labeled 'Use recommended performance settings'
• Uncheck another box named 'Use hardware acceleration when available'
• Then quit and restart Firefox

There you go. About a dozens of apparent and not-so-apparent tips should bring your Firefox to the best shape possible. And even if you don't experience many troubles with Firefox, following some tips above would help you optimize its speed and responsiveness. Best of all, you don't need a lot of third-party tool to perform a thorough checkup, and all the tools you need are easily available on Setapp.

Meantime, prepare for all the awesome things you can do with Setapp.

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This article describes what to do if Firefox doesn't open when you click the Firefox icon.

• If you get a message you can dismiss (e.g. 'TypeError: Components.classes['@ ... ;1'] is undefined', 'onload error TypeError: ...', 'Exc in ev handl: ...') and can open Firefox, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.
• If Firefox starts but won't load any websites, see Websites don't load - troubleshoot and fix error messages.

Table of Contents

• 1Specific error messages
• 2No error message

Mozilla Crash Reporter

If you get the 'Mozilla Crash Reporter' window when you start Firefox, see Troubleshoot Firefox crashes (closing or quitting unexpectedly) for solutions.

Firefox is already running but is not responding

See 'Firefox is already running but is not responding' error - How to fix for solutions.

Your Firefox profile cannot be loaded. It may be missing or inaccessible

See How to run Firefox when your profile is missing or inaccessible for solutions.

Failed to read the configuration file

This error is caused by a problem with Firefox program files. The solution is to remove the Firefox program and then reinstall Firefox. (This will not remove your passwords, bookmarks or other user data and settings which are stored in a separate profiles folder.)

1. Uninstall Firefox.
2. Delete the Firefox installation directory, found in one of these locations by default:
   • C:Program FilesMozilla Firefox
   • C:Program Files (x86)Mozilla Firefox
3. Use another browser to download the Firefox installer from the Firefox download page and install it. See How to download and install Firefox on Windows for details.

XULRunner - Error

If you see the message, 'XULRunner - Error: Platform version <x.x.x.x> is not compatible with minVersion <x.x.x.x>' ('<x.x.x.x>' depends on version number), after a software update, use another browser to download the Firefox installer from the Firefox download page, save it to the desktop or other location, delete the Firefox installation directory and then reinstall Firefoxreinstall Firefoxreinstall Firefox.

• If Firefox still does not start, see the Firefox will not start after updating section below.

There was an error launching the application

This error indicates that either Firefox is not installed or your shortcut to it is incorrect. Make sure that Firefox is installed at the location specified by the shortcut. If it isn't, install Firefox if necessary, then modify the shortcut to point to the correct location.

Error opening file for writing…

If you receive the above error when launching Firefox on a Windows system, you may be required by Firefox to log in as an administrator. You can either reboot the computer or, if you have an administrator account, you can execute the program as an administrator.

1. Find the firefox.exe program file in the Firefox application folder on your system.
2. Right-click the icon.
3. Select Run As….Select Run As Administrator…. Select The following user:. From the User name drop-down, select Administrator or another user that has administrator privileges. Enter the password required to log in to this account. Click .
4. The Firefox application is started using the administrator Windows account. The user that was used to log in to Windows at startup is still the active one.

Other error messages

If you get another error message (e.g. 'XML Parsing Error: undefined entity Location', 'Secure Connection Failed … uses an invalid security certificate'), see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.

If you click the Firefox icon but no Firefox window opens and no error message is shown, a simple first step is to restart your computer and then try again. If Firefox still does not start, see the following sections.

Firefox will not start after updating

• Outdated versions of Comodo Firewall or Comodo Antivirus security software (or a leftover file after Comodo was uninstalled) can cause Firefox not to start with no error message. Update Comodo to the latest version, if you have it installed. If Comodo software is not installed, check if there's a file called IseGuard64.dll or IseGuard32.dll in your C:Windowssystem32 folder or your system drive and, if so, manually delete the file.

• If you use certain versions of ZoneAlarm or other Internet security software that includes a 'Virtual Browsing' feature, it can prevent Firefox from starting. Check virtualization settings and clear the virtual cache, if your Internet security software includes this feature, or visit the software provider's support site for more help.
• Firefox may fail to start for some Windows users after updating, if AVG or AVAST antivirus is installed. For details, see this Techdows article.

Firefox will not start after installing add-ons

If Firefox previously worked but stopped after you installed extensions or themes, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.

Firefox previously worked

If Firefox previously worked but suddenly doesn't start, it may be due to some corrupt data in your settings. Uninstalling and reinstalling Firefox would not fix this problem because your settings are not removed on uninstall.

To test to see if this is the problem, use the Profile Manager to create a new profile. If the problem goes away, you can then move your bookmarks and other important settings into the new profile.

Disable Firewall Firefox Mac

Firefox will not start because of missing libraries

If you installed Firefox outside of your package manager, make sure that your system has the libraries listed in the system requirements.

Firefox Firewall Disable

Based on information from Browser will not start up (mozillaZine KB)