Add as bookmarklet (see below):
javascript:/* Reader Mode.js /(function(){ const IFWL=['gfycat.com','disqus.com','www.youtube.com',location.host,];const ifbl=new RegExp('derstandard\.at\/AdServer\/');const startupTasks=[disableViewport,];const periodicTasks=[disableStaticFloaters,removeIframes,];function disableStaticFloaters(){for(let e of document.getElementsByTagName('')){if(window.getComputedStyle(e).position.startsWith('fixed')){e.style.setProperty('position','static','important');}}}function removeIframes(){const iframes=getAllIframesRecursively();for(const e of getAllIframesRecursively().reverse()){try{const doRemove=(!e.src)? false : IFWL.indexOf(new URL(e.src).host)==-1 ? true : e.src.match(ifbl)? true : false;if(doRemove&&e.parentElement){e.parentElement.removeChild(e);}}catch(err){reportError(err,['FAILED TO REMOVE IFRAME',e]);}}window.readerModeRemainingIframes=getAllIframesRecursively();}function disableViewport(){const vp=document.querySelector('meta[name=v