In one of our customer web application, when we select any drop down control, the page freezes for 10-12 sec and page become unresponsive. After 12 sec, the page becomes back to normal. This is specifically happening when we accessing that control for first time. When accessing subsequent times, it works normal. We thought its due to volume of data, that is bound to the control. But its not. Its happening for drop down with 1 or 2 items. After analysis, we narrowed down that it is due to huge DOM content (13K nodes in DOM) loaded in initial page load. So, we cut down nodes to 7K and found minor improvement in page responsiveness. This functionality is working fine in Firefox browser up to version 54.0, with DOM size of 13K nodes. Post v54 up to latest v68, the problem started occurring that the page becomes unresponsive, when we select drop down. But, this functionality is working fine in Chrome browser without any lag with same amount of DOM loaded in it. ================== New observation on 30-Jul: When firefox is launched, the browser is launched with Default browser profile and the profile data are stored in local folder path "C:\Users\[username]\AppData\Roaming\Mozilla\Firefox\Profiles\3ozvc1f9.default" We observed that, if we delete all contents in default folder and launch the application in Firefox browser, the functionality is working fine, incredibly very normal & fast. Again if we logout & close browser window, open new browser window & access application, the page freeze when we access the drop down control. Until we cleanup default folder contents again, the issue occurs. If we clean the folder content, access application, page works, log out & login in same browser window, the issue does not occur. It appears that every time, we have to clean up default profile folder contents, if we access application in new browser window.