Sounds like you have a different app installed that is serving you ads, this is not a Firefox behaviour. Most likely it's from a game or wallpaper app that you have installed recently but with the state that mobile app development is in, it could be anything. Try removing any app that you have recently installed before getting this problem.

Thanks Zero,

I actually did go through my apps list but nothing supicious, worst case I will reset it to factory default :'(

Just out of curiosity, do you have anyany AdBlocker extensions installed in Firefox? If not, try installing 'uBlock Origin'. I've never heard of Firefox doing this before but if you have uBlock Origin installed and you still get pop up ads, then you'll know for sure that the problem isn't with Firefox.

No, I don't have it, in fact I haven't installed any add-on / extension to my firefox. I'll try and fingerscrossed can get it fixed.

Thanks again :)