I just have a bookmarklet to kill all "fixed" position divs.
I'm clicking it more and more these days - even those damn fixed navs that take up a stupid percentage of the screen give me the shits.
If clicking the bookmarklet doesn't get rid of your stupid modal newsletter sign up or annoying sticky nav, I'm just closing the tab.
Here's the bookmarklet btw:
javascript:(function()%7B(function () %7Bvar i%2C elements %3D document.querySelectorAll('body *')%3Bfor (i %3D 0%3B i < elements.length%3B i%2B%2B) %7Bif (getComputedStyle(elements%5Bi%5D).position %3D%3D%3D 'fixed') %7Belements%5Bi%5D.parentNode.removeChild(elements%5Bi%5D)%3B%7D%7D%7D)()%7D)()
You may also be interested in my filterlist[1] project for uBlock Origin which attempts to do this via CSS style overrides for many, many sites.