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Vaadin 7 is optimized to modern browsers, which inturn optimize rendering based on preprocessed dom-tree mostly working with div-elements. This is somewhat different to earlier HTML-dialects. Hence IE8 is quite slow almost anything done with modern tools since it optimizes rendering for HTML-tables etc. Moreover IE8 is mostly run with old computers, without the same computational resources than the new ones. However you can ease the burden of IE8 by making your UI layouts and component in fixed width. That will reduce amount of automatic width calculation logics quite a lot. So if you roughly know what is the screensize used by users, this could be feasible approach.