IEBlog : Designing for Add-on Performance

During startup, Internet Explorer checks the registry for installed add-ons. When IE detects an installed Browser Helper Object (BHO) or toolbar it calls CoCreateInstance to instantiate each installed and enabled add-on. Essentially, Internet Explorer creates add-ons as inproc servers, executing in the context of IE’s main UI thread. For backwards-compatibility Internet Explorer follows these steps for every opened tab. This behavior is important for several reasons, and you’ll see why as I discuss some of the most popular problems encountered by add-ons.

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