You may be infected with malware.

Do a malware check with some malware scanning programs.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
• https://support.mozilla.com/kb/Searches+are+redirected+to+another+site

If using the above listed scanners does not fix it or if you are blocked from installing those scanners then ask advice on one of the forums that specialize in malware removal mentioned in the Popups_not_blocked article.

Hi Cor-el and thanks for you reply.

Since developing the problem (no access to major sites like nytimes.com) I have run two complete scans using Norton Internet Security with the last run using latest 2012 version. Each time revealed no problems, no viruses, no malware. veloped right after the upgrade.

However the problem just went away! Don't understand, but not going to question it.

BTW: I did install FFv5 over v.6, but it didn't help. I am now back with v.6.

BTW: I meant to say in my post the FFv3.6 does not have the problem.