[CentOS] Firefox showing bogus sites after 'yum update'

I have just done a yum update for the first time in a while, and as part of 
that I believe Firefox got upgraded.

After the reboot I restarted Firefox which had been closed down with the 
option to retain all open tabs/windows.

However, when I restarted Firefox it had three new tabs, one being the ususal 
Firefox upgrade page. The other two were Phishing sites, one pretending to be 
Amazon the other I cannot remember.

Has anyone else experienced this?