I would like you to start Firefox in Firefox safe mode using the instructions below, and then do a search with Google, Bing, and Yahoo and let me know when you are still being redirected.
1. Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Exit menu item.
2. In Windows, click Start, open the All Programs list, and navigate to the Mozilla Firefox folder. In the Mozilla Firefox folder, select Mozilla Firefox (Safe Mode).
3. Firefox should start up with a Firefox Safe Mode dialog.
4. Click Continue In Safe Mode. This starts Firefox in its Safe Mode. While you are in Safe Mode, your extensions and themes will be disabled, and any toolbar customizations will be reverted back to their defaults. These changes are not permanent - when you leave Safe Mode and start Firefox up normally, your extensions, themes, and settings will return to the state they were in before you entered Safe Mode.