So have you gone into Tools>Add-Ons and seen whether it is installed there. ?
Have you got a "toolbar" installed with this...?
Do you have a host file installed?If not you could try MVPS host files,which will block a bunch of crap sites....
I understand you have run Malwarebytes...is that correct?
Edit: An excellent program for determining if you have hidden BHO,s (browser hidden objects) or toolbars is Win Patrol...available as free/paid......Look under "IE helpers"..(works on FFx too)....