Firefox will not open tabs in a window
Firefox won't open any tabs through "CTRL + T" or when you click on the "+" next to an open page. I have tried starting in safe mode and refreshing to many times. RIght clicking links to "open link in new tab" works fine though.
What security software do you have?
Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps.