This is usually a problem with a failed update that caused a corrupted installation that still has older files.

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

• Download the full Firefox installer and save the file to the desktop
  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 this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions.

Remove the Firefox program 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 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 for your quick response, however this doesn't help as I don't have the original discs, everything was already in place when I purchased my laptop, I decided in the end (around 2 this morning!) that I would download Google Chrome and got around it that way, I now have another problem, I can't delete Firefox from my laptop, have tried in Progs/Features etc all to no avail so if anyone has a solution to that I would be most grateful. Thanks.

You shouldn't have a need to use the Windows set up disks.

You would only need to delete the Firefox program folder to make sure that all files are removed before installig a freshly downloaded version of the Firefox installer.