Firefox may be struggling on a low spec machine with many addons installed (Or just other programs also running). Or it could be down mainly to interactions with security software. After an upgrade security related software may even prevent Firefox being used until the security software's settings are adjusted. * [[Firefox is slow - How to make it faster]] * [[Fix problems connecting to websites after updating Firefox]] * [[Configure Windows Firewall to allow Firefox access to the Internet]] What security related software do you use on the computer ? Did reading and trying suggestions in the above linked articles help ?