If you get blank popup boxes in WordPress, for example when using the visual editor you are unable to add or edit a link in posts, then try the following..

• Add your domain (like example.com, no need for the http or the www.) to the whitelist in your firewall or antivirus program that is blocking popups/ads/banners. I use Kaspersky, and to do this, go to Settings, Anti-Banner, then click on Settings and add your domain.
• Check your browser addons, some have URL checkers that could be causing a problem. I use FireFox with the Kaspersky URL Advisor Add-on. Try adding your domain to the exclusion list by clicking in FireFox – Tools, Add-ons, click on Options under Kaspersky URL Advisor, then add your domain to the exclusion list.
• Close and reload your browser.

This is another very good example of how a problem or setting change in one piece of software can impact on the performance of another piece of software.