title: GreaseMonkey - Firefox Web console not showing all javascript errors
body: <p>The Firefox Web console (<kbd>Ctrl</kbd> + <kbd>Shift</kbd> + <kbd>K</kbd>) is not showing all Javascript errors that are reported in the Firefox Error Console. How to change this?</p>
  
  <p>It's annoying because the Firefox Error Console has been deprecated and <a href="https://developer.mozilla.org/en-US/docs/Error_Console">needs to be re-enabled explicitely in Firefox configuration.</a></p>
  
  <p>Example of errors not showing in the Web console is accessing a property of an undefined object. This kind of exception just kills the Javascript running script and is very annoying to debug if it doesn't appear in the log...</p>
  
  <pre><code>var obj = undefined;
  obj['whatever'];
  </code></pre>
  
  <p>This will raise an error in the Error Console but not the Web console:</p>
  
  <pre><code>/*
  Exception: obj is undefined
  @Scratchpad/1:11
  */
  </code></pre>
  
  <p>Note that "JS > Errors" is checked in the Web Console and Chrome debugging is ON on the Web console configuration.</p>
  
  <p><strong>EDIT: This seems to only apply to GreaseMonkey userscripts (and scratchpad also).</strong></p>