It was not an easy one. As you can see from the posting time, I was up late at night. I started by creating new profiles, installing earlier versions, then Safe Mode, to no avail. But, since I could not access any websites, and the problem did not exist with other browsers, I decided to check the Firewall settings. All programs had a green(Allow) or yellow(Ask), for In or Out. Only Seamonkey had reds(Block) for both. For some reason my ISP mail was being delivered, but Yahoo and AOL were blocked. I have a hunch of the cause, but I can't prove it, yet.
UserAgent: Mozilla/5.0 (Windows NT 5.1; rv:9.0.1) Gecko/20111221 Firefox/9.0.1 SeaMonkey/2.6.1
A minority may be right, and a majority is always wrong. ~ Henrik Ibsen Win 10 HP Pavillion desktop , 8GB , Avast2016 , Zone Alarm Firewall, Seamonkey 2.42, Firefox 49.0.2, Thunderbird 45.4, also Toshiba Satellite laptop, 4GB, Win 10, , Chrome 51