Our current dEX web interface is not compatible to flash player plugin version 30 or newer, thus you will experience slow response on key stroke to the display. We will release the next version of dEX free of flash player, however for a time being you will need to downgrade flash player plugin from your web browser.
Some plugin is bundled with web browser such as Google Chrome, you will need to know the method to utilize older non-bundled version of flash player.
Download and install flash player version 29 from Adobe website: https://fpdownload.macromedia.com/pub/flashplayer/installers/archive/fp_184.108.40.206_archive.zip
After the above step you can run dEX without any issue.