Unfortunately, browsing with JavaScript disabled on mobile, I've noticed quite a large number of sites (usually WordPress blogs) that have the opt out button in the HTML, controlled server-side, so you have to enable JavaScript at least once to get rid of it.
Given that I prefer brave or bromite custom tabs (via Lynket) for short sessions on mobile (and prefer not to have long sessions on mobile at all), I generally just deal with it.
Most of those are implemented in JS, so NoScript goes a pretty long way to fixing this. It would be nice if Firefox somehow auto-detected them, and other useless pop-overs, and nuked them.