Easier just to ignore it completely, why should I waste my time on overriding their stupidity? Actually Google seem to be dropping them down the ranks, as I rarely see a Quora link now.
Off topic, but this code blob broke the formatting of the HN comment page, causing text to extend horizontally off the screen. It'd be great if you (or a mod) could add some (4, I think?) spaces in front of your code to make it appear in a code/pre tag.
javascript:(function(){function a(c){var e=document.getElementsByTagName('*'),i;for(i in e){if((' '+e[i].className+' ').indexOf(' '+c+' ')>-1){e[i].style.display="none";}}}a("modal_signup_background");a("modal_signup_dialog");a("modal_signup_facepile");})();