hello, could you go to the

• firefox menu > help > troubleshooting information,

copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

The System Details shows you are using Firefox 13.0.1 Is this true?

Download Firefox Full Installer All languages {web link}

If you really have the current version from mozilla.org which is Firefox 31.0 (thirtyone.zero) then perhaps your useragent is overridden to display as Firefox 13.0.1

https://support.mozilla.org/en-US/kb/websites-say-firefox-outdated-or-incompatible

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files against changes. If you have such software then check the settings or uninstall this software.

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

• Download the full Firefox installer and save the file to the desktop
  https://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 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 NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

If you keep having problems then also create a new profile.

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

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

Thanks for the reply. I am using Firefox 31.0. I tried this but when I right click on the relevant privileges, the reset bit is greyed out.

I don't have Advanced SystemCare installed. Will try the clean reinstall asap. Thanks.