Malware - clicking Google search results often redirects to advertisements

Running:

Windows Vista Home Premium sp2  - 32 bit

Firefox 3.6.14

Norton v18.5.0.125

 

Also scanned with:
MalwareBytes

ASquare

AVG

HijackThis

Kaspersky TDSSKill

None of these programs detect any infections or suspected malware. 

 

The only issue I'm having is that, when clicking on search results in Google searches, I am often redirected to advertisement web pages.  This occurs at random, roughly 1 time in 10.  Using the browser's back button and clicking the same result again will take me to the desired page.  Nothing undesirable exists in the hosts file.  All highjack this log entries are confirmed to be unrelated to this issue by multiple sources.

 

I've tried searching for known related files in C:/windows/system32, but so far, nothing associated with this infamous "Google Redirect Virus" can be found.  Also nothing in Device Manager associated with known-good information on this issue is present.  The following link is to a photobucket album containing screenshots of some of the pages I've been redirected to upon clicking legitamate Google results.  Hopefully someone here can provide me with some information about how to go about fixing this issue.  Thank you all for your time!

 

Photobucket Album containing screenshots of pages I've been redirected to.