How do i get rid of this Gamers Unite snag bar? Argh!

(have this problem on firefox not safari but hope this board might have an answer before i go nuts over this 😕)

How on earth do i delete this Gamers Unite snag bar? From years ago when i was into Facebook games but now i need to clean up my laptop for work and cant get this unprofessional looking thing unplastered from my browser head. Have spent hours going thru FAQs & threads & found lots of people with the same problem but no solutions. It seems they disabled the bar app/program awhile back and now that I've updated my laptop all the program files are gone- but the bar is still stuck on my browser, so you cant even get to a point to attempt an uninstall/trash, I've searched thoroughly, they're GONE! Aaargh! Have tried contacting GamersUnite, Mac, Firefox & other tech help boards to no avail praying someone out there has a fix because but this is so bad it seems like ill have to switch browsers entirely! (hope not, have firefox synced across all my devices) Thank you for your help-- L

(using newest version of firefox & OSX on macbook pro)

original app/bar issuer:

http://gamersunite.coolchaser.com/