This causes Chrome dev to crash.

twitterunread.user.js

// ==UserScript==
// @name           TwitterUnread
// @namespace      http://henrik.heimbuerger.de/greasemonkey/
// @description    [alpha01] ...
// @include        http://twitter.com/
// @include        http://twitter.com/#
// @include        http://www.twitter.com/
// @include        http://www.twitter.com/#
// @include        https://twitter.com/
// @include        https://twitter.com/#
// @include        https://www.twitter.com/
// @include        https://www.twitter.com/#
// ==/UserScript==

// TODO:
//  � better visual style for read tweets
//  � fallback for enhancing if the events all occur before the script can be loaded
//  � trigger initialization from an actual twttr pointcut instead of polling
//  � give the 'mark read' button its own icon
//  � only process the Home timeline, support switching between the streams, etc.
//  � store read state in the cloud
//  � support for Opera and Chrome

// wait for jQuery and twttr.app
function waiter() {
    if(unsafeWindow.jQuery && unsafeWindow.twttr
                           && unsafeWindow.twttr.app
                           && unsafeWindow.twttr.app.currentPage()
                           && unsafeWindow.twttr.app.currentPage().streamManager
                           && unsafeWindow.twttr.app.currentPage().streamManager.streams
                           && unsafeWindow.twttr.app.currentPage().streamManager.streams.current) {
        console.debug('ready');
        script(unsafeWindow.jQuery, unsafeWindow.twttr);
    } else {
        console.debug('waiting')
        setTimeout(waiter, 100);
    }
}
waiter();

function script($, twttr) {

    console.debug('start');

	/*
	 * Helper function for adding CSS to the current page
	 */
	function addGlobalStyle(css) {
		var head, style;
		head = document.getElementsByTagName('head')[0];
		if (!head) { return; }
		style = document.createElement('style');
		style.type = 'text/css';
		style.innerHTML = css;
		head.appendChild(style);
	}
	function addGlobalScript(code) {
		var head, script;
		head = document.getElementsByTagName('head')[0];
		if (!head) { return; }
		script = document.createElement('script');
		script.type = 'text/javascript';
		script.innerHTML = code;
		head.appendChild(script);
	}

    addGlobalStyle('.tweet-actions .mark-read-action span i{background-position:0 0;margin-right:0;margin-left:3px;}.tweet-actions .mark-read-action:hover span i{background-position:-16px 0;}');

    /*
     * jQuery.ScrollTo - Easy element scrolling using jQuery.
     * Copyright (c) 2007-2009 Ariel Flesler - aflesler(at)gmail(dot)com | http://flesler.blogspot.com
     * Dual licensed under MIT and GPL.
     * Date: 5/25/2009
     * @author Ariel Flesler
     * @version 1.4.2
     *
     * http://flesler.blogspot.com/2007/10/jqueryscrollto.html
     */
    console.debug('initializing $.scrollTo');
    addGlobalScript("(function(d){var k=d.scrollTo=function(a,i,e){d(window).scrollTo(a,i,e)};k.defaults={axis:'xy',duration:parseFloat(d.fn.jquery)>=1.3?0:1};k.window=function(a){return d(window)._scrollable()};d.fn._scrollable=function(){return this.map(function(){var a=this,i=!a.nodeName||d.inArray(a.nodeName.toLowerCase(),['iframe','#document','html','body'])!=-1;if(!i)return a;var e=(a.contentWindow||a).document||a.ownerDocument||a;return d.browser.safari||e.compatMode=='BackCompat'?e.body:e.documentElement})};d.fn.scrollTo=function(n,j,b){if(typeof j=='object'){b=j;j=0}if(typeof b=='function')b={onAfter:b};if(n=='max')n=9e9;b=d.extend({},k.defaults,b);j=j||b.speed||b.duration;b.queue=b.queue&&b.axis.length>1;if(b.queue)j/=2;b.offset=p(b.offset);b.over=p(b.over);return this._scrollable().each(function(){var q=this,r=d(q),f=n,s,g={},u=r.is('html,body');switch(typeof f){case'number':case'string':if(/^([+-]=)?\d+(\.\d+)?(px|%)?$/.test(f)){f=p(f);break}f=d(f,this);case'object':if(f.is||f.style)s=(f=d(f)).offset()}d.each(b.axis.split(''),function(a,i){var e=i=='x'?'Left':'Top',h=e.toLowerCase(),c='scroll'+e,l=q[c],m=k.max(q,i);if(s){g[c]=s[h]+(u?0:l-r.offset()[h]);if(b.margin){g[c]-=parseInt(f.css('margin'+e))||0;g[c]-=parseInt(f.css('border'+e+'Width'))||0}g[c]+=b.offset[h]||0;if(b.over[h])g[c]+=f[i=='x'?'width':'height']()*b.over[h]}else{var o=f[h];g[c]=o.slice&&o.slice(-1)=='%'?parseFloat(o)/100*m:o}if(/^\d+$/.test(g[c]))g[c]=g[c]<=0?0:Math.min(g[c],m);if(!a&&b.queue){if(l!=g[c])t(b.onAfterFirst);delete g[c]}});t(b.onAfter);function t(a){r.animate(g,j,b.easing,a&&function(){a.call(this,n,b)})}}).end()};k.max=function(a,i){var e=i=='x'?'Width':'Height',h='scroll'+e;if(!d(a).is('html,body'))return a[h]-d(a)[e.toLowerCase()]();var c='client'+e,l=a.ownerDocument.documentElement,m=a.ownerDocument.body;return Math.max(l[h],m[h])-Math.min(l[c],m[c])};function p(a){return typeof a=='object'?a:{top:a,left:a}}})(jQuery)");

    /*
     * jQuery AOP - jQuery plugin to add features of aspect-oriented programming (AOP) to jQuery.
     * http://jquery-aop.googlecode.com/
     *
     * Licensed under the MIT license:
     * http://www.opensource.org/licenses/mit-license.php
     *
     * Version: 1.3
     *
     * Cross-frame type detection based on Daniel Steigerwald's code (http://daniel.steigerwald.cz)
     * http://gist.github.com/204554
     */
    console.debug('initializing $.aop');
    addGlobalScript("(function(){var j=1;var k=2;var l=3;var m=4;var n=5;var o=6;var p=true;var q='arguments';var r='undefined';var s=(function(){var toString=Object.prototype.toString,toStrings={},nodeTypes={1:'element',3:'textnode',9:'document',11:'fragment'},types='Arguments Array Boolean Date Document Element Error Fragment Function NodeList Null Number Object RegExp String TextNode Undefined Window'.split(' ');for(var i=types.length;i--;){var b=types[i],constructor=window[b];if(constructor){try{toStrings[toString.call(new constructor)]=b.toLowerCase()}catch(e){}}}return function(a){return a==null&&(a===undefined?r:'null')||a.nodeType&&nodeTypes[a.nodeType]||typeof a.length=='number'&&(a.callee&&q||a.alert&&'window'||a.item&&'nodelist')||toStrings[toString.call(a)]}})();var t=function(a){return s(a)=='function'};var u=function(b,c,d){var f=b[c];if(d.type!=o&&!t(f)){var oldObject=f;f=function(){var a=arguments.length>0?q+'[0]':'';for(var i=1;i<arguments.length;i++){a+=','+q+'['+i+']'}return eval('oldObject('+a+');')}}var h;if(d.type==j||d.type==k||d.type==l)h=function(){var a,exceptionThrown=null;try{a=f.apply(this,arguments)}catch(e){exceptionThrown=e}if(d.type==j)if(exceptionThrown==null)a=d.value.apply(this,[a,c]);else throw exceptionThrown;else if(d.type==k&&exceptionThrown!=null)a=d.value.apply(this,[exceptionThrown,c]);else if(d.type==l)a=d.value.apply(this,[a,exceptionThrown,c]);return a};else if(d.type==m)h=function(){d.value.apply(this,[arguments,c]);return f.apply(this,arguments)};else if(d.type==o)h=function(){return d.value.apply(this,arguments)};else if(d.type==n){h=function(){var a={object:this,args:Array.prototype.slice.call(arguments)};return d.value.apply(a.object,[{arguments:a.args,method:c,proceed:function(){return f.apply(a.object,a.args)}}])}}h.unweave=function(){b[c]=f;pointcut=b=h=f=null};b[c]=h;return h};var v=function(a,b,c){var d=[];for(var f in a){var g=null;try{g=a[f]}catch(e){}if(g!=null&&f.match(b.method)&&t(g))d[d.length]={source:a,method:f,advice:c}}return d};var w=function(a,b){var c=typeof(a.target.prototype)!=r?a.target.prototype:a.target;var d=[];if(b.type!=o&&typeof(c[a.method])==r){var e=v(a.target,a,b);if(e.length==0)e=v(c,a,b);for(var i in e)d[d.length]=u(e[i].source,e[i].method,e[i].advice)}else{d[0]=u(c,a.method,b)}return p?d:d[0]};$.aop={after:function(a,b){return w(a,{type:j,value:b})},afterThrow:function(a,b){return w(a,{type:k,value:b})},afterFinally:function(a,b){return w(a,{type:l,value:b})},before:function(a,b){return w(a,{type:m,value:b})},around:function(a,b){return w(a,{type:n,value:b})},introduction:function(a,b){return w(a,{type:o,value:b})},setup:function(a){p=a.regexMatch}}})()");

    console.debug('plugin initialization complete');

	var LOCAL_STORAGE_KEY_LAST_READ_TWEET_ID = 'lastReadTweetID';
	var TWITTER_ATTRIBUTE_TWEET_ID = 'data-item-id';
    var MAX_FETCH_MORE = 3;
    var hasScrolled = false;
    var isCurrentlyEnhancing = false;

    function getLastReadTweetID() {
        console.debug('retrieving last read tweet ID: ' + localStorage.getItem(LOCAL_STORAGE_KEY_LAST_READ_TWEET_ID));
        return localStorage.getItem(LOCAL_STORAGE_KEY_LAST_READ_TWEET_ID);
    }

    function setLastReadTweet(tweetID) {
        console.debug('setting last read tweet ID to: ' + tweetID);
        localStorage.setItem(LOCAL_STORAGE_KEY_LAST_READ_TWEET_ID, tweetID);
    }

    function executeWithLastReadTweet(callback, fetchCycleCounter) {
        if(!fetchCycleCounter) fetchCycleCounter = 0;

        console.debug('Searching for last read tweet, currently on iteration ' + fetchCycleCounter + '/' + MAX_FETCH_MORE);

        foundTweet = $('div.stream-item[data-item-id="' + getLastReadTweetID() + '"]').get(0);
        if(foundTweet) {
            console.debug('found: ' + foundTweet);
            callback($(foundTweet));
        } else if(!foundTweet && fetchCycleCounter < MAX_FETCH_MORE) {
            console.debug('fetching more...');
            twttr.app.currentPage().streamManager.getMoreOldItems(function() {executeWithLastReadTweet(callback, fetchCycleCounter+1);});
        } else {
            console.debug('giving up search');
        }
    }

    function onMarkReadActionClick() {
        var tweet = $(this).parents('div.stream-item');
        var tweetID = tweet.attr(TWITTER_ATTRIBUTE_TWEET_ID);
        console.log('marking as read until ' + tweetID);
        setLastReadTweet(tweetID);
        blurOutReadTweets(tweet);
    }
    
    function onJumpHomeClick() {
        executeWithLastReadTweet(function(lastReadTweet) {
            scrollToTweet(lastReadTweet.next());
        });
    }

    function blurOutReadTweets(lastReadTweet) {
        if(lastReadTweet) {
            console.log('blurring from ' + lastReadTweet.attr(TWITTER_ATTRIBUTE_TWEET_ID));
            lastReadTweet.nextAll().andSelf().css('opacity', '0.3');
            // in case the user is trying to 'mark unread'
            lastReadTweet.prevAll().css('opacity', '1.0');
        } else {
            alert('last read tweet not found');
        }
    }

    function scrollToTweet(tweet) {
        if(tweet) {
            console.log('scrolling to ' + tweet.attr(TWITTER_ATTRIBUTE_TWEET_ID));
            $.scrollTo(tweet, {
                axis: 'y',                     // no horizontal scrolling please
                duration: 1500,                // scrolling should be visible to give the user feedback on the current situation
                easing: 'swing',			   // just makes it look a bit nicer
                offset: -window.innerHeight    // we want that tweet to be at the *bottom* of the screen
            });
        }
    }

    function enhanceWithAction(result) {
        if(!isCurrentlyEnhancing) {
            isCurrentlyEnhancing = true;
            console.group('enhancing');

            // add the new actions
            $('span.tweet-actions:not(.enhanced)')
                // make sure they are only enhanced once
                .addClass('enhanced')
                // add the 'mark read until here' action
                .append('<a class="mark-read-action" href="#"><span><i></i><b>Mark read until here</b></span></a>')
                // add the click handlers
                .children('a.mark-read-action').click(onMarkReadActionClick);

            console.groupEnd();
            
            executeWithLastReadTweet(function(lastReadTweet) {
                // blur out read tweets
                blurOutReadTweets(lastReadTweet);

                // on the first load, also scroll to the last unread tweet (plus one, so we see where the list of unread tweets ends)
                if(!hasScrolled) {
                    scrollToTweet(lastReadTweet.next());
                    hasScrolled = true;
                }
            });

            isCurrentlyEnhancing = false;
        }

        return result;
    }

    function initHooks() {
        // hook into the tweet loading
        $.aop.after({target: twttr.app.currentPage().streamManager.streams.current, method: 'onShowOldItems'}, enhanceWithAction);
        $.aop.after({target: twttr.app.currentPage().streamManager.streams.current, method: 'onShowNewItems'}, enhanceWithAction);
        
        // the logo is used to just jump to your current reading state
        $('#logo').unbind('click').click(onJumpHomeClick);
    }
    initHooks();

}

This userscript developed by Henrik Heimbuerger. Latest version.