I have uBlock Origin and Privacy Badger installed on Firefox, and I can just click anywhere outside that window to see the full article. Not sure it's to do with the browser extensions necessarily, but I don't have a particularly exotic setup.

The only other thing I have which might help is a user chrome file - https://www.userchrome.org/how-create-userchrome-css.html - which has this simple rule in it:

  html, body { overflow-y: visible !important; }

That seems to help with a lot of the basic "disable scrolling" css rules that sites use.