This article describes what to do if the Firefox window 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]]. __TOC__ = Specific error messages = == Mozilla Crash Reporter == If you get the "''Mozilla Crash Reporter''" window when you start Firefox, see [[Firefox crashes - Troubleshoot, prevent and get help fixing crashes]] for solutions. == Firefox is already running but is not responding == See [["Firefox is already running but is not responding" error message - How to fix it]] 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. == 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 [http://www.mozilla.org/firefox mozilla.org/firefox], save it to the desktop or other location, delete the Firefox installation directory and then {for win}[[Installing Firefox on Windows|reinstall Firefox]]{/for}{for mac}[[Installing Firefox on Mac|reinstall Firefox]]{/for}{for linux}[[Installing Firefox on Linux|reinstall Firefox]]{/for}. * If Firefox still does not start, see the [[#w_firefox-will-not-start-after-updating|Firefox will not start after updating]] section below. {for linux} == 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, [[Installing Firefox on Linux|install Firefox]] if necessary, then modify the shortcut to point to the correct location. {/for} {for win} == 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. # Find the {filepath firefox.exe} program file in the Firefox application folder on your system. # Right-click the icon. #{for winxp}Select {menu Run As…}.{/for}{for win7,win8}Select {menu Run As Administrator…}.{/for} 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 {button OK}. # 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. {/for} {for mac} == Firefox.app can't be opened because the identity of the developer cannot be confirmed == If you see this error after installing Firefox, see [[Firefox can't be opened after you install it on a Mac - How to fix]] for solutions. {/for} == 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]]. = No error message = 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 == *If Firefox fails to start after an update, first check the [[Latest Firefox issues|Firefox Hot topics]] section to see if it contains a solution. *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 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 [[Use the Profile Manager to create and remove Firefox profiles|Profile Manager]] to create a new profile. If the problem goes away, you can then [[Recovering important data from an old profile|move your bookmarks and other important settings into the new profile]]. {for mac} == Firefox will not start on OS X 10.4 or earlier or with a PowerPC processor == See [[Firefox no longer works with Mac OS X 10.4 or PowerPC processors]]. {/for} {for linux} == 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 [http://www.mozilla.org/firefox/system-requirements.html system requirements]. {/for} <!-- MZ credit --> <br/> <br/> '''''Based on information from [http://kb.mozillazine.org/Browser_will_not_start_up Browser will not start up (mozillaZine KB)]'''''

This article describes what to do if the Firefox window 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.

Specific error messages

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.

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 mozilla.org/firefox, 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.

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.

No error message

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

• If Firefox fails to start after an update, first check the Firefox Hot topics section to see if it contains a solution.
• 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 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.

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