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Firefox Developer Edition. Get the Firefox browser built just for developers. Check out the home for web developer resources. Firefox Reality. Explore the web with the Firefox browser for virtual reality. Donate your voice so the future of the web can hear everyone. The Firefox cache temporarily stores images, scripts, and other parts of websites you visit in order to speed up your browsing experience. This article describes how to clear the cache. To clear your history (cookies, browsing history, cache, etc.) all at once, see Delete browsing, search and download history on Firefox. Firefox Developer Edition d iminig arurrad ugar n wiyaḍ, yegber ifecka n tneflit n tsuta taneggarut akked timahilin timaynutin am usefrek n twezza CSS neɣ tamseɣtayt n uframework.

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.

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.

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

The Browser Console is like the Web Console, but applied to the whole browser rather than a single content tab.

So it logs the same sorts of information as the Web Console - network requests, JavaScript, CSS, and security errors and warnings, and messages explicitly logged by JavaScript code. However, rather than logging this information for a single content tab, it logs information for all content tabs, for add-ons, and for the browser's own code.

Firefox Developer Exe

If you also want to use the other web developer tools in the regular Web Toolbox with add-on or browser code, consider using the Browser Toolbox.

Similarly, you can execute JavaScript expressions using the Browser Console. But while the Web Console executes code in the page window scope, the Browser Console executes them in the scope of the browser's chrome window. This means you can interact with all the browser's tabs using the gBrowser global, and even with the XUL used to specify the browser's user interface.

NB: The Browser Console command line (to execute JavaScript expressions) is disabled by default. To enable it set the devtools.chrome.enabled preference to true in about:config, or set the 'Enable browser chrome and add-on debugging toolboxes' (Firefox 40 and later) option in the developer tool settings.

Opening the Browser Console

You can open the Browser Console in one of two ways:

1. from the menu: select 'Browser Console' from the Web Developer submenu in the Firefox Menu (or Tools menu if you display the menu bar or are on macOS).
2. from the keyboard: press Ctrl+Shift+J (or Cmd+Shift+J on a Mac).

You can also start the Browser Console by launching Firefox from the command line and passing the -jsconsole argument:

The Browser Console looks like this:

You can see that the Browser Console looks and behaves very much like the Web Console:

• most of the window is occupied by a pane that display messages.
• at the top, a toolbar enables you to filter the messages that appear.
• at the bottom, a command line interpreter enables you to evaluate JavaScript expressions.

Beginning with Firefox 68, the Browser Console allows you to show or hide messages from the content process (i.e. the messages from scripts in all the opened pages) by setting or clearing the checkbox labeled Show Content Messages. The following image shows the browser console focused on the same page as above after clicking on the Show Content Messages checkbox.

Browser Console logging

The Browser console logs the same sorts of messages as the Web Console:

• Warnings and errors (including JavaScript, CSS, security warnings and errors, and messages explicitly logged by JavaScript code using the console API)
• Input/output messages: commands send to the browser via the command line, and the result of executing them

However, it displays such messages from:

• web content hosted by all browser tabs
• the browser's own code
• add-ons

Messages from add-ons

Firefox Developer Tools Shortcut

The Browser Console displays messages logged by all Firefox add-ons.

Console.jsm

To use the console API from a traditional or bootstrapped add-on, get it from the Console module.

One exported symbol from Console.jsm is console. Below is an example of how to access it, which adds a message to the Browser Console.

Learn more:

HUDService

There is also the HUDService which allows access to the Browse Console. The module is available at Mozilla DXR. We see we can not only access the Browser Console but also Web Console.

Here is an example on how to clear the contents of the Browser console:

If you would like to access the content document of the Browser Console this can be done with the HUDService. This example here makes it so that when you mouse over the 'Clear' button it will clear the Browser Console:

Bonus Features Available

For Add-on SDK add-ons, the console API is available automatically. Here's an example add-on that just logs an error when the user clicks a widget:

If you build this as an XPI file, then open the Browser Console, then open the XPI file in Firefox and install it, you'll see a widget labeled 'Error!' in the Add-on bar:

Click the icon. You'll see output like this in the Browser Console:

For Add-on SDK-based add-ons only, the message is prefixed with the name of the add-on ('log-error'), making it easy to find all messages from this add-on using the 'Filter output' search box. By default, only error messages are logged to the console, although you can change this in the browser's preferences.

Browser Console command line

The Browser Console command line is disabled by default. To enable it set the devtools.chrome.enabled preference to true in about:config, or set the 'Enable chrome debugging' option in the developer tool settings.

Like the Web Console, the command line interpreter enables you to evaluate JavaScript expressions in real time:Also like the Web Console's command line interpreter, this command line supports autocomplete, history, and various keyboard shortcuts and helper commands. If the result of a command is an object, you can click on the object to see its details.

But while the Web Console executes code in the scope of the content window it's attached to, the browser console executes code in the scope of the chrome window of the browser. You can confirm this by evaluating window:

This means you can control the browser: opening, closing tabs and windows and changing the content that they host, and modify the browser's UI by creating, changing and removing XUL elements.

Controlling the browser

The command line interpreter gets access to the tabbrowser object, through the gBrowser global, and that enables you to control the browser through the command line. Try running this code in the Browser Console's command line (remember that to send multiple lines to the Browser Console, use Shift+Enter):

It adds a listener to the currently selected tab's load event that will eat the new page, then loads a new page.

Note: You can restart the browser with the command Ctrl + Alt + R (Windows, Linux) or Cmd + Alt + R (Mac) This command restarts the browser with the same tabs open as before the restart.

Modifying the browser UI

Since the global window object is the browser's chrome window, you can also modify the browser's user interface. On Windows, the following code will add a new item to the browser's main menu:

On macOS, this similar code will add a new item to the Tools menu: