[jQuery] "async: false is not defined" - error

[Ivan]

I'm getting this error

"async: false is not defined"

with Firebug 1.05 turned on

I need to post content of the textarea (not the whole form) via Ajax,
the code follows:
---
function preview()
{
        var content = $("textarea#profile_content").val();
        var preview_text = $.ajax({
        type: "POST",
        url: "preview.php",
        data: "profile_content=" + escape(content),
        async: false
        }).responseText;

        $("div#preview_area").html(preview_text);
}
---
With Firebug turned off everything works fine.

Browser is: Firefox 2.0.0.3
JQuery is: 1.1.2

Please could you help me?

Ivan