I had this too - lots of random words underlined and leading to advertising links. Turns out the most recent update I did of Mozilla had this attached to it - but it was easily located in my Programs (as Yontuu) and is gone now....I think!!
HURRY, ENTRIES CLOSE TODAY! A magical hour of storytelling and sing-alongs with Julia from her best-loved storybooks, including The Gruffalo, What the Ladybird Heard, Room on the Broom and The Snail and the Whale. Win Melbourne, Geelong & Sydney tickets.