Q:

Why this is executed twice?

I have code like this:
$(document).ready(function() {

    $("div #covert, div #coverb").height($(window).height() / 2 + 1);
    $(window).resize(function() {
        $("div #covert, div #coverb").height($(window).height() / 2 + 1);
        covconcr();
    });

    function covconcr() {
        $('div #covercon').css('left', $(window).width() / 2 - $('#covercon').width() / 2);
    }

    covconcr();

    function hidecover() {
        var goup = $('div #covert').height();
    }

    $("div #covercon").fadeOut("fast").fadeIn("fast").fadeOut("fast").fadeIn("fast").fadeOut("fast").fadeIn("fast").fadeOut("fast").fadeIn("fast").fadeOut("fast").delay(100).fadeIn("fast", function() {
        $(this).stop();
    });

    $('title').html('Drink86_browser.detection');

    var logoop;

    jQuery.each(jQuery.browser, function() {
        if ($.browser.msie) {
            $('div #covercon').delay(3000, function() {
                $(this).html("YOUR BROWSER IS: INTERNET EXPLORER.");
                $('title').html('Drink86_your.browser.is.internet.explorer');
            });
        }
        else if (!$.browser.msie) {
            function update() {
                //$('#site').load('site.php');
                $('div #covercon').html("YOUR BROWSER IS: " + jQuery.uaMatch(navigator.userAgent).browser + ".");
                covconcr();
                $('title').html('Drink86_your.browser.is.' + jQuery.uaMatch(navigator.userAgent).browser + ' ');

                function hidecov() {
                    $('title').html('Drink86_loading_files');
                    $('#covercon').html($('#loading').html());
                    covconcr();
                    var timer = setInterval(function() {
                        $("#loadingpro").html(Math.round($("#progress").width() / 4) + "%");
                    }, 20);
                    $("#progress").animate({
                        width: 400
                    }, 2000, function() {
                        $('title').html('Drink86_');
                        clearInterval(timer);
                        $('#covercon').delay(700).fadeOut('fast', function() {
                            //    if(logoop!="yes"){
                            $('#logobig').css('left', $(window).width() / 2 - $('#logobig').width() / 2).css('top', $(window).height() / 2 - $('#logobig').height() / 2);
                            $('#logobig').fadeIn(3000).delay(2500).fadeOut(3000);
                            logoop = "yes";
                            // }
                        });
                    });
                }
                setTimeout(hidecov, 1000);
            }
            setTimeout(update, 3100);
        }
    });
});

operation with #logobig (fadeIn and fadeOut) is executed twice.
why?
i had previous issues similiar to those but then they were executed twice just in Firefox.
any ideas why?

A:

What exactly were you thinking with
jQuery.each(jQuery.browser, function() { ...

That really makes no sense. Just look at jQuery.browser (if you must).
Also, checking to see if it's IE in an "if" statement, and then if it's not IE in the "else" part, well, again ...
The direct answer to your question is that jQuery.browser probably has two things in it, so you do that stuff twice.

A:

I think your problem is that you are iterating through the collection of jQuery's browser flags, which is not necessary to accomplish what you are doing.  If you were looking at the page in Firefox, the second clause of your if/elseif would execute on every loop, since the value never changes. Try removing that function from the each loop, so that it just looks like this:
if ($.browser.msie) {
    $('div #covercon').delay(3000, function() {
        $(this).html("YOUR BROWSER IS: INTERNET EXPLORER.");
        $('title').html('Drink86_your.browser.is.internet.explorer');
    });
} else if (!$.browser.msie) {
    function update() {
        //$('#site').load('site.php');
        $('div #covercon').html("YOUR BROWSER IS: " + jQuery.uaMatch(navigator.userAgent).browser + ".");
        covconcr();
        $('title').html('Drink86_your.browser.is.' + jQuery.uaMatch(navigator.userAgent).browser + ' ');

        function hidecov() {
            $('title').html('Drink86_loading_files');
            $('#covercon').html($('#loading').html());
            covconcr();
            var timer = setInterval(function() {
                $("#loadingpro").html(Math.round($("#progress").width() / 4) + "%");
            }, 20);
            $("#progress").animate({
                width: 400
            }, 2000, function() {
                $('title').html('Drink86_');
                clearInterval(timer);
                $('#covercon').delay(700).fadeOut('fast', function() {
                    //    if(logoop!="yes"){
                    $('#logobig').css('left', $(window).width() / 2 - $('#logobig').width() / 2).css('top', $(window).height() / 2 - $('#logobig').height() / 2);
                    $('#logobig').fadeIn(3000).delay(2500).fadeOut(3000);
                    logoop = "yes";
                    // }
                });
            });
        }
        setTimeout(hidecov, 1000);
    }
    setTimeout(update, 3100);
}

