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 [[Troubleshooting extensions and themes]]. * If Firefox starts but won't load any websites, see [[Error loading web sites]]. __TOC__ = Specific error messages = == Mozilla Crash Reporter == If you get the "''Mozilla Crash Reporter''" window when you start Firefox, see [[Firefox crashes]] for solutions. == Firefox is already running but is not responding == See [[Firefox is already running but is not responding]] 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 [[Installing Firefox|reinstall Firefox]]. * 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} == The program must close to allow a previous installation attempt to complete == If you get a message saying ''"The program must close to allow a previous installation attempt to complete. Please restart."'' when you start Firefox, see [[The program must close to allow a previous installation attempt to complete]]. == 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. #* '''(Windows 2000/XP)''' Select {menu Run As...}. 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}. #* '''(Windows 7 and Vista)''' Select {menu Run As Administrator...}. Complete a similar set of steps, as those listed above. # 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} == 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 [[Troubleshooting extensions and themes]]. = 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]] article 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 [[Troubleshooting extensions and themes]]. == 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 [[Managing 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,fx4} == 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 win} {for not fx13} == Firefox will not start on Windows 98/ME or earlier == Mozilla has stopped supporting Windows 98/ME and earlier. None of these operating systems are supported by Microsoft (and have not been for quite some time) and have multiple vulnerabilities that will remain unpatched. As such, you have the following option: * You can update to Windows XP, Windows Vista or Windows 7. If you don't want to pay for a new operating system or if your hardware is too old to be updated, you can install a [http://en.wikipedia.org/wiki/List_of_Linux_distributions Linux distribution] which can run on older machines. This ensures you have a completely secure system and access to all the great new features in Firefox. {/for} {for fx13} == Firefox will not start on Windows 2000/XP SP1 or earlier == Depending on your version, see [[Firefox no longer works with Windows 2000]] or [[Firefox no longer works with some versions of Windows XP]]. {/for} {/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/en-US/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.

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 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 Latest Firefox issues article 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.

Firefox will not start on Windows 98/ME or earlier

Mozilla has stopped supporting Windows 98/ME and earlier. None of these operating systems are supported by Microsoft (and have not been for quite some time) and have multiple vulnerabilities that will remain unpatched. As such, you have the following option:

• You can update to Windows XP, Windows Vista or Windows 7. If you don't want to pay for a new operating system or if your hardware is too old to be updated, you can install a Linux distribution which can run on older machines. This ensures you have a completely secure system and access to all the great new features in Firefox.

Firefox will not start on Windows 2000/XP SP1 or earlier

Depending on your version, see Firefox no longer works with Windows 2000 or Firefox no longer works with some versions of Windows XP.

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