Firefox opens multiple tabs while clicking on "Manage account" under File- Account in Office 2013 opens the right Tab and another random URL-Tab

Question

I have office 365 installed. When I click on Manage Account under File->Accounts in office 2013, it opens 2 Tabs in Firefox.
Tab1: https://office.microsoft.com/MyAccount.aspx?ver=15&app=winword.exe&MachineKey=02011-005-827906&fromAR=1
Tab2: http://www.4a1.com/ ( which is random)
The version of firefox is 24 and set as the default browser.
Operating System: Windows 7SP1
Already contacted Internet Service provider-Optimum, also the antivirus for security concerns but could not find anything from their end respectively.
The issue occurs on Windows 8 laptop also.

Answer 1

Thank you for your reply.
(FYI: The above question was posted by a ''Microsoft Research Engineer'' and me since neither of us can figure out why this is happening. So the brain-bank on this is pretty big!)
I scanned with all of the above scanners. (Thank you for the links!)
I also scanned my system with Adaware, Super Antispyware, Norton Internet Security 2013, and Norton Power Eraser . . . and Kapersky v14 on the Windows 8 system)
NONE of the scanners reported anything other than the usual trackers.
Firefox was un-installed, re-installed, reverted back 4 versions ''and'' v3. Chrome shows the same result.
The Windows 8 system was wiped and restored. Office 365 was immediately re-installed and showed the SAME behavior except that the "random" 3-character URL was different . . .
. . . This extra Tab ''only'' shows up when I open any Office 2013 product to a New document or worksheet go to File>Account>Manage Account.