I cannot open Yahoo or Google or other websites with Firefox or Safari on my Mac. I cannot open Apple either. I made sure the proxies were not checked, I emptied history and cache and cookies, I reset Safari, I restarted each time I did these things. But I cannot get my mail on Yahoo or Google. I could open CNN or NFL or Fox only! IS there anything else I can do? This is on an older Mac 10.5.8.
Might check your system's hosts file. See http://osxdaily.com/2012/08/07/edit-hosts-file-mac-os-x/ and be sure to create a backup copy of the file before doing any editing.