here some of print_r($GLOBALS['browser']); if it helps
Horde_Browser Object
(
     [_majorVersion:protected] => 5
     [_minorVersion:protected] => 0
     [_browser:protected] => mozilla
     [_agent:protected] => Mozilla/5.0 (X11; U; Linux i686; fr; 
rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7
     [_lowerAgent:protected] => mozilla/5.0 (x11; u; linux i686; fr; 
rv:1.9.1.7) gecko/20091221 firefox/3.5.7
     [_accept:protected] => 
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
     [_platform:protected] => unix
    [_features:protected] => Array
         (
             [html] => 1
             [hdml] =>
             [wml] =>
             [images] => 1
             [iframes] => 1
             [frames] => 1
             [tables] => 1
             [java] => 1
             [javascript] => 1,4
             [dom] => 1
             [utf] => 1
             [rte] => 1
             [homepage] =>
             [accesskey] => 1
             [optgroup] => 1
             [xmlhttpreq] => 1
             [cite] => 1
             [dataurl] => 1
             [ischrome] =>
             [iskonqueror] =>
             [issafari] =>
         )

     [_quirks:protected] => Array
         (
             [avoid_popup_windows] =>
             [break_disposition_header] =>
             [break_disposition_filename] =>
             [broken_multipart_form] =>
             [buggy_compression] =>
             [cache_same_url] =>
             [cache_ssl_downloads] =>
             [double_linebreak_textarea] =>
             [empty_file_input_value] =>
             [must_cache_forms] => 1
             [no_filename_spaces] =>
             [no_hidden_overflow_tables] =>
             [ow_gui_1.3] =>
             [png_transparency] =>
             [scrollbar_in_way] =>
             [scroll_tds] =>
             [windowed_controls] =>
         )

Got it! at last...

compress_pages is set to true by default in 
conf.php.dist:$conf['compress_pages'] = true;
disabling this option gets rid of the "headers already sent" messages.

this warnings occurs after calling framework/Horde/Horde.php:1628 
ob_start('ob_gzhandler');

You can't. This ticket state doesn't mean that you are not willing to 
give any feedback, but that there isn't sufficient information given 
to fix the problem.

how should i provide any feedback when i get no more information when 
running the application?

Without any hint about where the output has started, there isn't 
anything we could do.

I do see this as well when I access kronolith or DIMP.
PHP Warning:  Cannot modify header information - headers already sent 
in Unknown on line 0, referer: 
http://x.x.x.x/horde/services/portal/sidebar.php

I don't see this using IMP or turba.
I use apps from git and FF 3.5.5.
I've cleared cache,prefs and cookies.

I don't see this.

everytime i execute a command through Adminstration -> Command two 
entries appear in my php.log file

[10-Nov-2009 10:10:03] PHP Warning:  Cannot modify header information 
- headers already sent in Unknown on line 0