In addition to above, some observations. 1. I changed:
$.blockUI ({ message: $('#inner-holder-error'), css: { top: ($(window).height() - 500) /2 + 'px', left: ($(window).width() - 500) /2 + 'px', width: '500px', height: '500px' } }); to: $.blockUI ({ message: $('#inner-holder-error'), css: { top: ($(window).height() - $('#inner-holder- error').height()) /2 + 'px', left: ($(window).width() - $('#inner-holder- error').width()) /2 + 'px' } }); to force displaying centered message no matter of it's dimensions. But this fails as either $('#inner-holder-error').height() returns incorrect value (759 pixels in my situation, where 308 px should be) or blockui changes div width AFTER displaying it. Effect - message still not being centered vertically. 2. I used some jquery UI inner classes for forcing theming as I would like to see it (what theme: true does is not what I want to see) and was very surprised that block UI ignores round corners on FF for two of four sides. See example: http://trejderowski.pl/trash/blockui-2.jpg Really strange I must admit. 3. Did you noticed / were aware that any alert('') places AFTER blockUI call will be displayed BEFORE block UI blocks page? Cheers, T.