I have had this problem for a couple of months. I fixed it today by "disabling" the extension Xulrunner 1.9.1. Seem this is a bogus entry and is the source of the redirecting (at least in my case). I used trial and error after trying all of the other methods posted everywhere on the internet. I disabled all of my extensions and turned them on one by one while doing a Google search after each one was turned back on. Xulrunner 1.9.1 was the one that resatrted the redirecting. Easy to try it yourself.

As mentioned above, look in your Firefox add-ons to see if the bogus XULRunner 1.9.1 add-on has been installed.

Here's how I went about permanently removing it:

• Go to the URL 'about:support'.

• Note the ID of XULRunner.

• Close Firefox.

• Search for the corresponding registry entry. You should find the value under HKEY_CURRENT_USER\Software\Mozilla\Firefox\Extensions\{<add-on ID here>} .

• Note the path in the registry key value.

• Delete the registry entry.

• Go to the path that you just noted. It should read something like:C:\Users\<your user name>\AppData\Local\<add-on ID here>

• Delete that folder.

Some extra precautionary housekeeping, if you like:

• Within the file C:\Users\<your user name>\AppData\Roaming\Mozilla\Firefox\Profiles\o0bi5lzk.default\extensions.rdf

• ...locate the RDF:Description block that contains the add-on ID. Note the RDF:resource value.

• Now delete the entire RDF block.

• Do the same with the corresponding RDF:Seq RDF block.

• Search for the RDF:Description block that contains the RDF:resource value noted above. Delete that block.

Test Firefox:

• Reopen Firefox.

• Check your add-ons to be sure that the XULRunner entry no longer exists.

• Search Google and ensure that searching for a popular term, such as 'antivirus' not longer redirects you via google.ad.sgdoubleclick.net. As a bonus, you should also find that that Google Instant Search has returned to operation.