Possible solution. Clear ALL history (absolutely everything from the beggining of time), disconnect from your Google account/Firefox so it doesn't pull something back in. Reset browser to default settings (Chrome is Advanced->"reset" Firefox https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems) and disable add-ons.
At the very least this should reset your add preferences and make it show up less often.
At the very least this should reset your add preferences and make it show up less often.