We are having a page, heavily loaded with devexpress comboboxes in a gridview. And that gridview is inside the detail row of a master gridview. On the change of values in master gridview, values of comboboxes of inner gridview gets changed using the callback but it takes too long. And due to the default settings of dom.max_script_run_time at client machine, it starts giving the message that "A script on this page may be busy, or it may have stopped responding.".
However, I suggest you read our Performance - How to improve the page rendering speed KB article to learn how to improve page performance.