When you use Internet Explorer 11 to browse websites that use a proxy PAC file, the browsing may delay. This is caused when Internet Explorer 11 sometimes queries for a domain name that begins with the "dummy" word.
To resolve this problem, install the most recent cumulative security update for Internet Explorer. To do this, go to Microsoft Update. Additionally, see the technical information about the most recent cumulative security update for Internet Explorer.
Note This update was first included in March cumulative security update for Internet Explorer (MS15-018).
This issue occurs because the cross-origin checks cannot accommodate the blob protocol that is used by web workers.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
See the terminology that Microsoft uses to describe software updates.