Question

Check this link.
http://dev.twitter.com/pages/share_bookmarklet

Drag bookmarklet to your bookmark-bar and click on it. It will open a pop up window.

Why is my firefox/ie/chrome not blocking this?

Thanks

javascript: 
function loadScript(scriptURL) {
    var scriptElem = document.createElement('SCRIPT');
    scriptElem.setAttribute('language', 'JavaScript');
    scriptElem.setAttribute('src', scriptURL);
    document.body.appendChild(scriptElem);
}
var url = 'http://api.bit.ly/shorten?version=2.0.1&login=tweetthees&apiKey=Rxyz&longUrl=' + document.location;
var longUrl = document.location;
loadScript(url + '&callback=tweetme');
function tweetme(json) {
    var shortLink = json.results[longUrl].shortUrl;
    var finalUrl = 'http://twitter.com/home?status=Reading: ' + document.title + ' ' + shortLink;
    window.open(finalUrl, "Share link", "width=1024,height=400,location=1,status=1,scrollbars=1");
}

Answer 1

Usually popup-blocker don’t block popups general, they only block popups that should be opened without any user-action. Thats not the case if you use bookmarklets, because the user selects the bookmarklet before the popup opens. When using a bookmarklet it may be, that this would’nt get observed by a popup-blocker, like Nick said(I think there is no need to, a bookmarklet should be trusted).

But in a webpage this popup also would’nt be blocked, if the function was called following a click-event.