In my admin panel I have 2 instances of fckeditor (2.6.4), but in ff11 the second instance isn't visible. In other browsers (including ff10) don't have this problem.
$oFCKeditor = new FCKeditor('ps_short_description') ;
$oFCKeditor->Width = '600';
$oFCKeditor->Height = '300';
$oFCKeditor->BrowserPath = SHOP_WWW_PATH.'/upload/fck_files';
$oFCKeditor->Value = "";
$oFCKeditor->Create() ;
$oFCKeditor = new FCKeditor('ps_description') ;
$oFCKeditor->Width = '600';
$oFCKeditor->Height = '500';
$oFCKeditor->BrowserPath = SHOP_WWW_PATH.'/upload/fck_files';
$oFCKeditor->Value = "";
$oFCKeditor->Create() ;
HTML code in ff11 and ff9 is the same (Firebug).
How to deal with this problem?
At this point, the simplest thing to do may be to wait 11 days until Firefox 12 is released. This bug is fixed in Firefox 12.