When reporting a performance problem with Firefox, or when experiencing instances of Firefox stuttering or otherwise being unresponsive to input, obtaining a snapshot of what's going on during that period is extremely helpful for developers. This page will walk you through using the freely available AMD CodeAnalyst tool to create such a snapshot.
Download and Install AMD CodeAnalyst
Download AMD CodeAnalyst for Windows from AMD's Developer site. (You may need to create an account.) Make sure you download the latest version, which at the time of this writing is 2.94. The download site is a little unclear, often offering links to multiple versions.
Start a Profiling Run
Start CodeAnalyst by double-clicking its icon. You'll see the following screen: