Hi This is an issue caused by Symantec (the people who make Norton) not getting an update out fast enough. They have said that an update is due by the end of October, so hopefully it is due soon. I would always recommend you use the most recent and and up to date version of Firefox. This ensures you get the new features plus any stability and security fixes. I hope this helps, but if not, please come back here and we can look into a different solution for you.