One of the most common causes for slow performance in Expression Web is network latency while remotely authoring a site. For example, if you are editing your site live using an HTTP or FTP path, the performance of Expression Web while doing so is heavily reliant on the speed of the connection between you and your web server. Your Internet connection may be plenty fast, but if the connection to your hosting company is slow, editing in Expression Web will be slow. To resolve this kind of problem, you should edit your site using a local, disk-based copy and then publish changes to the server periodically.
Expression Web can also perform slowly if your graphic card’s drivers aren’t up to date. Expression Web uses a technology called Windows Presentation Foundation (WPF) to display the user interface. WPF relies on hardware acceleration in your graphics card for optimized performance, and if the drivers you are using aren’t updated, you may encounter performance problems. Make sure that you update your drivers through Windows Update or from your graphics card manufacturer.
Finally, we’ve recently discovered a bug in Expression Web that can cause poor performance when you have CSS elements that use the clear property and there are no CSS floats on the page. To work around this issue, always make sure that there is at least one element using the CSS float property if you are using the clear property.