Try Scan your PC:

• Problems caused by malwares

Case the problem persist try disable the McAfee only for test, because in Brazilian Forum other user had the same problem that yours and the problem was cause by McAfee

thanks for that, but not possible to turn off 'Mcafee all access protection' without removing complete system. I have been running them together for several months with no problem unless yesterday's update is the problem..... by trying it after backdating the computer and blocking Mcafee updates would be a test but surely everyone running Mcafee with Firefox would have the same problem and it would affect many more people?

There may be a Disable For X Minutes in its menu.

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Start Firefox in Safe Mode

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Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

You might need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

Then perform these steps:

• Click the orange Firefox button at the top left, then select the "Options" button, or, if there is no Firefox button at the top, go to Tools > Options.
• In the Firefox options window click the Advanced tab, then select "General".
• In the settings list, you should find the Use hardware acceleration when available checkbox. Uncheck this checkbox.
• Now, restart Firefox and see if the problems persist.

Additionally, please check for updates for your graphics driver by following the steps mentioned in the following Knowledge base articles:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

• Upgrade your graphics drivers to use hardware acceleration and WebGL

Did this fix your problems? Please report back to us!

Thank you.

I can now only start Firefox in compatibility mode for Windows 95 which is weird as I am running XP. If I try and open 'options' Firefox instantly crashes. I am also now getting a Microsoft Visual C++ Runtime error message R6025. along with Internet Explorer Script error '$ is undefined'... I am running SP3

LAST RESORT ! ! Reset Firefox

Thanks but done that....three times! Tried removing it again, then another new download saved into a new file then cancelling hardware acceleration and it still runs perfectly once and will not re-start except in Win 95 compatibility which will not do searches or allow any personalisation.

Thanks but done that....three times! Tried removing it again, then another new download saved into a new file then cancelling hardware acceleration and it still runs perfectly once and will not re-start except in Win 95 compatibility which will not do searches or allow any personalisation.

Well, I'm out of ideas. Anyone else out there have anything?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 27: http://www.mozilla.org/en-US/firefox/all.html

If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you lose personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Thanks but been through that, done full remove with fresh install into new folder. Even resorted to trying remove all personal data on re-install.

Did you have this problem with prior versions of Firefox? Or is this the first FF you have? I was thinking that you should completely remove FF, then install a prior version just to see if it works or not. Instill Old Versions Of Firefox

I have tried another total remove including old Firefox folders, and re-installed older version. Same problem, opens on download then will not open again unless set to run as Win 95 or 98 compatible. Watching Windows Taskmaster, the 'Firefox.exe' start appears, stays for about two seconds then just vanishes. I have run Firefox for years along with Mcafee with no previous problems.

Try reinstalling Firefox again and then disable all plugins in the Firefox Add-ons Plugins list before restarting Firefox (see Disable or remove Add-ons). If Firefox can then be restarted, one of the plugins you disabled is the likely cause.

http://kb.mozillazine.org/Browser_will_not_start_up#Problematic_plugin_prevents_browser_from_starting

Thanks for that, but already tried. Have now after several more attempts, removed every last piece of existing Firefox installs I could find, cancelled auto update and installed Firefox 21.0 which is currently running ok and re-starting with plugins....still have no idea what is causing the problem but I suspect it must be part of the Win XP prof system. That may explain all the different error messages I have received during installs, start attempts and system backdating?

Just to cover all bases, did you actually try cor-el's suggestion,

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

.... to see if Firefox 27 will run in Windows Safe Mode with Networking, before you downgraded to Firefox 21? See this Microsoft article for Windows XP Safe Mode information. Running Firefox 21 or other outdated Firefox versions is a bad solution because of security vulnerabilities.

Anyway, now that Firefox is running,

1. Enter about:plugins in the Firefox address bar to see a list of all installed plugins. Are these the plugins you said you disabled? They would have been set to "Never Activate" in the Add-ons -> Plugins list, if you disabled them. (Even though you said you disabled all plugins, maybe you meant Add-ons -> Extensions?)
2. It may also help if you could copy-paste Firefox Troubleshooting Information here. See Use the Troubleshooting Information page to help fix Firefox issues

I think you are on to something there Alice and Smailholm. I tried to summarize to understand what has been tried and put reference for what errors you saw meant(as vague as some can be)

Th three errors:

• parsing error: programming (code) is in the process of being translated by the compiler and there is an error in the coding
• runtime error Runtime error message R6025: error in C++ when the function call is not valid http://support.microsoft.com/kb/125749
• xml error- this should not show up in safe mode if you disabled hardware acceleration
• error page- turn off debugging scipts in ie and that should go away http://support.microsoft.com/kb/308260 ehow http://www.ehow.com/how_4922612_fix-ie-error.html

already have tried:

• reinstalling and clean install
• resetting Firefox
• safe mode
• malware and virus scan
• windows safe mode in windows 95 compatibility mode?
• Microsoft safe mode? Diagnostic tools to use in windows safe mode http://www.ehow.com/how_4922612_fix-ie-error.html

And now currently the computer is running Firefox 21. So to better understand what is different that may be causing the errors before is to provide a new list of troubleshooting info.(Alice's comment above)

I have no add-ons. all plug-ins disabled. Hardware acceleration switched off. tried running safe mode ( you are correct, no xml warning in safe mode or with add-ons disabled) also set Program Access to show Firefox as default browser. I guess I will just have to retire and devote my life to tracking this down! Thanks for all your help, much appreciated. cheers