(function () {
    "use strict";
    var settings, display;

    if (window !== window.top) {
        return;
    }

    safari.self.tab.dispatchMessage('getSettings');

    safari.self.addEventListener('message', function (event) {
        if (event.name === 'settings') {
            settings = event.message;

            if (settings.blacklist.indexOf(window.location.hostname) !== -1) {
                display = document.documentElement.style.display;
                document.documentElement.style.display = 'none';
                window.setTimeout(function () {
                    document.documentElement.style.display = display;
                }, 1000 * (settings.delay - settings.jitter + (Math.random() * 2 * settings.jitter)));
            }
        }
    }, false);
}());

@@ -44,22 +44,25 @@
 ttings, 
-displa
+visibilit
 y;%0A%0A    
@@ -404,22 +404,25 @@
         
-displa
+visibilit
 y = docu
@@ -448,22 +448,25 @@
 t.style.
-displa
+visibilit
 y;%0A     
@@ -511,23 +511,28 @@
 yle.
-display = 'none
+visibility = 'hidden
 ';%0A 
@@ -633,24 +633,30 @@
 yle.
-displa
+visibilit
 y = 
-displa
+visibilit
 y;%0A 

Switch from "display:none" to "visibility:hidden".