title: Why does my WebGL context only have a subset of extensions
body: <p>I'm working on a rewrite of some of the rendering internals of an existing WebGL application. All of a sudden, the <code>WEBGL_depth_texture</code> extension is no longer available within my rendering context (which is inconvenient, as I need it for this particular application).</p>
  
  <p>If I open up antother tab in the same browser (<em>Chrome 58.0.3029.110 (64-bit)</em>) and look at the WebGL Caps Viewer (<a href="http://www.geeks3d.com/webgl/" rel="nofollow noreferrer">http://www.geeks3d.com/webgl/</a>), I see the proper set of <em>24</em> extensions including <code>WEBGL_depth_texture</code>. </p>
  
  <p>In my own application, I now have a meagre subset of <em>9</em> extensions available to me. </p>
  
  <p>I obviously broke something, but how do I investigate what is wrong? </p>