Does that happen in Firefox safe mode? Maybe an extension is causing it?

This problem is here netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect"); inside the extension

Where do you see that error?
Are you visiting specific websites or use bookmarklets or others JavaScript code?

UniversalXPConnect is no longer supported in current Firefox releases, so if you visit a web page that uses it then this won't work anymore. Extensions don't need this and shouldn't cause this error because they already run code with chrome privileges.

• bug 546848 - Remove support for enablePrivilege

(please do not comment in bug reports)

i'm getting the same error too every time i open up firefox on my laptop windows 7 and i keep getting this.

Error: TypeError: netscape.security.PrivilegeManager is undefined

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Как только обновил браузер стало появляться это окно всегда при запуске мозилы - фаерфокс: приложение: Java Script Error: TypeError: netscape.security.PrivilegeManager is undefined

Что это значит и что делать?

Hi kritimer

As posted above, the security manager is no longer supported in current Firefox versions, so if a web page or possibly an extension is still using this to perform actions that require chrome privileges then it is no longer possible to get this privilege.
Only extensions will be able to perform such actions.

Go to Tools: Add-ons: Click on disable AVG Security toolbar

I have disabled the AVG toolbar which has stopped the error message but I can't get into my Hotmail page, I get the message :"We can't connect to Hotmail right now, try again later". Also I bookmarked the TV Guide and now can only see the evening programmes for the current day - I can't view earlier times or following days. Please help - a simply as possible as I am a senior and not very computer savvy,

This worked and then I re-enabled the AVG toolbar and problem seems to have gone away.

Thanks for the help, Everything went back to normal by itself, then I had the same problem with Internet Explorer which also corrected itself and then the problem cropped up in my neighbours' computer! All too confusing for us seniors!