If that problem is with both Firefox5 and IE8, it is probably caused by a Virus or by Malware on your PC.

Run a full, deep scan with your Anti-Virus application. If that doesn't find it and remove it, run a complete Malware scan.

Install, update, and run these programs in this order. They are listed in order of efficacy.
(Not all programs detect the same Malware, so you may need to run them all to solve your problem.)
These programs are all free for personal use, but some have limited functionality in the "free mode" - but those are features you really don't need to find and remove the problem that you have.
Note: If your Malware infection is bad enough and you are mis-directed to URL's other than what is posted, you may have to use a different PC to download these programs and use a USB stick to transfer them to the afflicted PC.

Malwarebytes' Anti-Malware - http://www.malwarebytes.org/mbam.php
SuperAntispyware - http://www.superantispyware.com/
AdAware - http://www.lavasoftusa.com/software/adaware/
Spybot Search & Destroy - http://www.safer-networking.org/en/index.html
Windows Defender: Home Page - http://www.microsoft.com/windows/prod.../default.mspx
Also, if you have a search engine re-direct problem, see this:
http://deletemalware.blogspot.com/2010/02/remove-google-redirect-virus.html

If these don't find it or can't clear it, post in one of these forums for specialized malware removal help:
http://www.spywarewarrior.com/index.php
http://forum.aumha.org/
http://www.spywareinfoforum.com/
http://bleepingcomputer.com

Just go to show, you get what you pay for in this world. I ask an informed solution and I get this mambo jumbo!Is this the best you can come up with! At least you could of recommended a OS upgrade. Never mind that most sites are doing major upgrading to incorporate android, etc. There are millions of lines of code, with ever 0;1 percent errors will cause problems for millions. In the decades I've been programming, I've never heard a "expert" blame software code, or compatibility errors, As if code has some how become error free. When you don't know, always safe to blame a virus.Hell they can find a virus, even when they are not there.Anything to sell another useless anti-virus program.

My computer is clean. I do run Search and Destroy and adAware all the time. Which are great free programs.I also run clean my PC and several other scans regularly. I also have some sophisticated  monitoring of processes. 

I have found that I can reach these site on the same computer, but different I.S.P. Name a malware in any library that can accomplish that. This are site related errors.

Thank for the list anyway. Always good to have another reference.